How to Build a DIY Plunge Pool: The Ultimate Guide

Last updated: September 2026

A plunge pool in the back garden is one of the best things you can build. It’s small enough to be a realistic DIY project, big enough to cool off in on a hot day, and if you heat it, you can use it most of the year. And yes, it’s easier to build than you think.

A quick word on where my experience comes from. My own build is an in-ground block hot tub, and the method for a plunge pool is exactly the same: dig, slab, walls, plumbing, waterproofing, tiles. The main differences are scale and depth. So throughout this guide I use my own build as the example, and I’ve added what I’ve learned since from helping more than 1,500 people build their own tubs, plunge pools and cocktail pools.

What is a plunge pool?

A plunge pool is a small, deep-ish pool built for cooling off, soaking and relaxing rather than swimming lengths. There’s no strict definition, but most are somewhere between 3m and 6m long (10–20ft) and about 1.2–1.5m (4–5ft) deep. That’s enough to stand up in with your shoulders under the water. Checkatrade’s 2026 guide describes UK plunge pools as anything from 1.5m x 1.5m up to about 1.5m x 5m, and 1m to 2.5m deep.

The names get muddled, so here’s how I use them:

Type	Typical size and depth	Typical water temperature	Used for
Hot tub	2–3m (7–10ft) square, ~1m (40in) deep, with seats	37–40°C (98–104°F)	Hot soaking with jets
Plunge pool	3–6m (10–20ft) long, 1.2–1.5m (4–5ft) deep	Unheated to about 30°C (86°F)	Cooling off, wading, a swim jet if it’s long enough
Cocktail pool or spool	Similar to a plunge pool, with benches, loungers and often jets	Pool temperature in summer, can be run hotter in winter	Socialising with a drink in hand
Cold plunge	Usually one person, 1–1.2m deep	Kept cold, often with a chiller	Short cold immersions

If you’re still deciding which to build, read Hot tub vs plunge pool: which should you build in 2026? For the cocktail pool version, with loungers and jets, see Build the ultimate DIY cocktail pool or spool.

Can you build a plunge pool yourself?

Yes, if you’re a reasonably confident DIYer and willing to plan properly. I’d never laid a block before my build. I was slow, but it worked. The parts that need real care are the structure, which has to hold many tonnes of water without cracking, and the electrics, which you should leave to a qualified electrician. It’s perfectly normal to do most of the work yourself and hire in a digger, a bricklayer for a few days or a concrete pump.

What does it cost?

Professionally installed plunge pools aren’t cheap. In the USA, Angi’s 2026 guide puts the average at about $28,000, with most people paying $10,000–$40,000, and concrete pools running from $20,000 to $75,000. In the UK, Checkatrade puts a concrete in-ground plunge pool at £15,000–£25,000 plus labour, with a heater adding £1,200–£2,600.

DIY is a fraction of that, but I’m not going to give you a single figure. It depends on size, finishes, heating and how much you hire in, and prices have changed a lot since I built mine. Price your own parts list before you start. That’s one of the things my plans give you.

Plan it properly before you dig

If the planning is done right, the rest of the build is so much easier. I learned the hard way by not leaving enough space for my control room, which is where the pump and electronics go. I’ve since had to rebuild it.

Location

• Filling and topping up. You’ll lose water to evaporation and splashing, so you need a tap nearby. A hose works, but a fill pipe built into the pool looks far neater. An auto top-up is even better.
• Emptying it. You won’t be watering the flowers with treated pool water. Where’s the nearest drain, and will you use a submersible pump or build drainage into the plumbing?
• The view. If you can face a view rather than a fence, do it.
• The control room. Pumps, filters, heaters and pipes take up space. Keep it close to the pool to keep pipe runs short.
• Power. Where will the supply come from, and what route will the cable take? Plan it before you pour concrete across it.
• Services. Check for buried cables and pipes. In the UK, use LinesearchbeforeUdig, and in the USA call 811.

In-ground or above ground?

Personally, I prefer in-ground. I wanted things as minimal as possible in the garden, and I liked the idea of dropping into the ground rather than being on display for the neighbours. A raised or semi-raised pool involves less digging, but the walls have to resist the full water pressure with nothing behind them. That needs proper reinforcement and, ideally, an engineer’s sign-off. Semi-in-ground (half dug in, with a seating-height wall) is a nice compromise.

Outdoors, under a roof or indoors?

If you’re planning a roof or a building over the pool, decide now, because the footings go in with the groundworks. Indoors, the big issue is humidity. You need proper ventilation and a dehumidifier sized for the room, plus insulation and a vapour control layer, or you’ll get condensation, mould and rot.

Size, depth, shape and features

• Depth. Around 1.2–1.4m (4ft–4ft 6in) of water suits most adults for standing and cooling off. Remember that the hole has to be much deeper than the water (more on that below).
• Steps and benches. Built-in steps make getting in and out safer, and a bench along one side turns a plunge pool into a cocktail pool.
• Shape. Blocks and ICF are square, so rectangles are by far the easiest to build and to tile. Curves are possible, but the more ambitious the shape, the harder the tiling.
• A swim jet. If you want to swim, a counter current swim jet turns a plunge pool into a mini exercise pool. The pool needs to be at least 4m (14ft) long, or the wave bounces back off the far wall. Plan it now, because it needs its own pump and pipework. See swim jet considerations and how to install a counter current swim jet.

My plunge pool / cocktail pool plans come in seven standard sizes, from 10ft x 7ft up to 20ft x 10ft. Each one includes architectural drawings, plumbing layouts, steps and a lounger area, plus a build guide and videos, in imperial and metric.

Permissions and safety barriers

UK

In England, the Planning Portal says an outdoor domestic pool often doesn’t need planning permission, because it’s treated as permitted development under the outbuildings rules. Those rules say no more than half the land around the original house can be covered and that nothing can go forward of the front of the house. You’ll need to check with the council for listed buildings, conservation areas, national parks and other designated land. Wales, Scotland and Northern Ireland have their own rules. Whatever the planning position, the electrics are notifiable under Part P.

USA

Almost everywhere in the USA, an in-ground pool needs a building permit, plus electrical inspection and a compliant safety barrier. Your city or county decides which code it adopts, so start there. There’s more in Do I need a permit for my hot tub?, and the same process applies to pools. My plans include architectural drawings that you can take to the permit office.

Safety barriers and fencing

A plunge pool is deep enough to drown in, and small children are drawn to water.

	USA	UK
Is a barrier required?	Yes, in most places. Most jurisdictions base their rules on the ISPSC or IRC, and some states add their own.	No law requires one for a private pool, but RLSS UK recommends secure fencing at least 4ft high.
Height	At least 48in, and 5ft or more is preferable (CPSC). Some areas require 60in.	1.2m (4ft) or more is sensible.
Gaps	No gap a 4in sphere can pass through, and no more than 4in under the fence on a hard surface (2in on grass).	Follow the same logic. No footholds, and nothing a toddler can squeeze through or climb.
Gates	Self-closing and self-latching, opening outwards away from the pool, with the latch high up or on the pool side.	Same, ideally lockable.
Covers and alarms	A powered safety cover meeting ASTM F1346 is accepted in some cases, for example where the house wall forms part of the barrier. Check locally.	A rigid, lockable cover plus a pool alarm are good extra layers, but they don’t replace supervision.

Rules vary by state, county and city, so check with your local building department before you build. In the UK, check your home insurance too, as some insurers have their own conditions for pools. And whatever the law says, RLSS UK’s point that most child drownings happen when there’s no adult supervising is the one to remember.

Digging out

This is where the fun really begins. Because of the access to my back garden, there was no way to get a digger round, so mine was dug by hand. It was back-breaking stuff. It took about two weeks of evenings and full weekends, and there was a lot of rubble and clay to move.

Once the ground got harder, I bought a mid-range electric breaker for around £200. It was the best money I spent on the whole build. You can hire bigger ones, but I didn’t know how long I’d need it and didn’t want to pay for something sitting idle. What I’d do today: check whether a micro digger will fit through the side gate. For a plunge pool, which moves far more soil than my tub did, a digger is almost essential.

A few tips:

• Dig deeper than the water. Add the freeboard, tiles, membrane, render, slab, insulation, DPM and sub-base, which is typically 350–400mm (14–16in) more. Dig to the water depth and your steps and benches end up too shallow.
• Don’t work in a deep hole with sides that could collapse. Clay stands up well, but sand and loose fill don’t. Batter the sides back or support them.
• Plan the spoil. Soil bulks up by around a third once it’s dug. A 4m x 2.5m (13ft x 8ft) plunge pool, allowing for the walls and a little working room, dug to about 1.8m, is roughly 25–30m³ in the ground and a third more once it’s out. That’s a lot of skips or grab lorries, so sort it out before day one.
• If you hit water, stop and think. A high water table is exactly why the hydrostatic relief valve matters (see below).

There’s more on this stage in my DIY in-ground hot tub build guide.

The structure: base, rebar, walls and waterproofing

I’d done electrics before, and plumbing is “kitchen plumbing on steroids”. What worried me was the structure: could I build a hole that wouldn’t leak or give way under the weight? My tub holds about 2,800 litres, which is 2.8 tonnes of water. A 4m x 2.5m plunge pool with 1.3m of water holds around 13,000 litres (about 3,400 US gallons), which is 13 tonnes. So the structure has to be right.

1. Sub-base and membrane

Lay 100–150mm (4–6in) of compacted Type 1 (MOT) sub-base. I only put in about 60–70mm and tamped it with a heavy bit of timber and a sledgehammer. Hire a plate compactor instead, as it’s cheap and far better. The sub-base spreads the load so the slab doesn’t crack, and cracks mean leaks.

I then laid a thick PVC pond liner over the gravel. It did the job, but today I’d use a thin layer of sand blinding and a proper 1200-gauge polythene damp-proof membrane (DPM), lapped, taped and turned up the sides. Add rigid, compression-rated insulation under the slab if you’re going to heat the pool.

2. Hydrostatic relief valve and main drains

Everything that goes through the floor has to be in place before you pour.

• Hydrostatic relief valve. If groundwater builds up under the pool while it’s empty, it can lift or crack the shell. The valve opens and lets that water in rather than letting the pressure build. It’s cheap and easy to fit now, and very hard to add later. See Why do I need a hydrostatic relief valve?.
• Twin main drains. Two drains mean that if one gets blocked it won’t ruin your pump, but the far more important reason is safety. A single drain with strong suction can trap a person underwater (hair, limbs or body entrapment). Fit two drains teed into one suction line, at least 1m (3ft) apart, with anti-entrapment covers. In the USA, the Virginia Graeme Baker Act requires public pools to have drain covers meeting ANSI/APSP/ICC-16, and a secondary anti-entrapment measure where there’s a single drain or drains less than 3ft apart. Follow the same standard at home. See Installing a main drain.
• Sleeves for any pipes or cables that cross under the slab.

3. Rebar and the slab

I used steel rebar tied together with wire. A builder might have called it overkill, but I was worried about strength and leaks. For a plunge pool it isn’t overkill at all. It’s essential. Use a grid on spacers so it sits in the middle of the slab, not on the bottom, and leave starter bars sticking up where the walls go so the walls and floor act as one structure. My rebar guide covers bar sizes and spacing.

Now the confession. I mixed my slab by hand, barrow after barrow, at roughly 4 parts sand to 1 part cement with plenty of waterproofing additive. It’s held, but 4:1 sand and cement is a mortar or screed mix, not structural concrete. For a plunge pool, order ready-mix concrete (C25/C30), pour the slab in one go to avoid cold joints, and aim for at least 150mm (6in). For a deep pool, a pool near a house or a site with a high water table, get a structural engineer to set the spec.

4. Walls: block, ICF or shotcrete?

You’ll see gunite and shotcrete pools all over YouTube. They’re great to watch, but spraying concrete is specialist work. For DIYers the realistic choices are:

• Concrete block. This is what I used, and it works. For a plunge pool, use hollow blocks with vertical rebar tied into the starter bars and core-fill them with concrete, or use solid dense blocks with the wall backed by concrete. On strength, I went with middle-of-the-road 7N blocks, which was fine for my shallow tub. For a deeper pool, follow your plans or engineer.
• ICF (insulated concrete form). If I built again, I’d use ICF without hesitation. It’s like Lego for adults: the forms dry-stack, one person can build the walls, and once they’re filled with concrete you get a strong, insulated, reinforced wall in one go. See the best ICF blocks for a hot tub or pool.
• Poured concrete. This is very strong but needs formwork. There’s a full comparison in Hot tub wall construction: what are the options?

Blockwork tips from someone who’d never laid a block

• Get the first course square. Mine ended up about 2cm out because I didn’t put guide lines in properly at the start. Measure both diagonals, and if they match, you’re square.
• Start on a level base. The deepest part of mine wasn’t 100% level, and I spent ages compensating. By the second course I had guide lines in, and the top courses finished perfectly square.
• Mortar consistency matters. I mixed at about 4–5 parts sand to 1 part cement, slightly wetter than normal because I was slow. Too wet, though, and heavy blocks won’t sit properly.
• Pick dimensions that use whole blocks, and order spares, because blocks split when you cut them and shatter when you drop them. My tub (2.3m x 2.6m) took about 100 blocks.
• A hand block saw cost me about £15 and made mincemeat of the blocks. For a big pool with lots of cuts, hire a disc cutter.

Wall penetrations: returns, skimmer and swim jet

Every return, jet and light needs a gunite body (wall fitting) set into the wall. Core drilling block with an ordinary drill was harder than I expected, because the bit bounces around until it’s 5mm in. My trick was to cut a “U” in a spare block, hold it in place with my foot as a guide, and drill through it. In ICF it’s far easier: cut the foam and set the fitting before you pour. Two lessons:

• Glue the pipes into the gunite bodies before you set the bodies in the wall. Doing it afterwards is fiddly.
• Keep every body square to the wall. A few of mine aren’t, and the jet faces don’t sit flush. Nobody else notices, but it niggles me.

There’s a step-by-step in the ultimate guide to gunite jet body installation.

5. Backfill

My logic was that if the blockwork has nowhere to move, it can’t move. So I poured concrete behind the walls, over the pipework and gunite bodies, and used the block offcuts as filler. For a plunge pool, backfill with concrete or well-compacted granular fill, as your plans specify, and pressure test the buried pipework before you bury it.

6. Waterproofing: render, membrane, flood test

When I built mine, I added waterproofing liquid to every mix and sealed the render with PVA. Today I’d do it differently. Additives help, but they aren’t a waterproofing system, and PVA isn’t designed to be permanently underwater. The modern approach is:

1. Waterproof render on block walls (a scratch coat and a float coat) to give a flat, sound surface.
2. A pool-rated membrane in two coats. In the UK and Europe, Ardex S 7 Plus is made for waterproofing pools before tiling. In the USA, Laticrete Hydro Ban is approved for in-ground concrete pools and submerged use. Follow the data sheet for primers, coverage and cure times.
3. A flood test before you tile. Fill it, mark the level, and leave it for a few days. It’s far easier to fix a leak now than behind finished tiles.

Most paint-on membranes are designed to hold water in, not keep groundwater out from behind, which is another reason for the hydrostatic relief valve. See waterproofing, grout and tile adhesive.

Plumbing and equipment

The idea is simple. Water is drawn from the skimmer at the surface and the main drains at the bottom, goes through the pump and filter, then through the heater and sanitiser, and back into the pool through the return inlets. In a hot-tub-style setup, the cartridge filter usually sits on the suction side before the pump. In a traditional pool setup, a sand or cartridge filter sits after the pump. My plans include layouts for both.

Pipe

• Use pressure-rated PVC, with proper fittings. “Flexible” pipe isn’t very flexible. I tried to bend it up through the steps to avoid joints, thinking more joints meant more leaks. I was wrong. A properly made solvent-weld joint is very reliable, and neat, square runs leak far less than awkward bends. See how to make the perfect PVC solvent weld joint.
• Don’t mix imperial and metric. They look almost identical, but they aren’t. For example, 1½in imperial pipe is 48.3mm across the outside, while metric pool pipe is 50mm. That’s enough to ruin a joint under pressure. Stick to one system and use proper adaptors where you have to change. I used a couple on my skimmer, which was metric while the rest of my system was imperial.
• Leave access to every joint in the control room. I knew exactly where my first leak would be: an awkward joint on a funny angle that I couldn’t quite reach. Sure enough, that’s where it dripped.

Skimmer

The skimmer sets your water level, which should sit about halfway up the mouth. I got two things wrong: I underestimated its height once I’d added a 90° bend underneath, and had to break out another 20cm (8in) of concrete, and the lid didn’t end up flush with the deck I added later. Plan the finished deck height first. I used a Certikin pool skimmer, which is the right choice for a plunge pool. See how to install a skimmer on a DIY hot tub or plunge pool.

Pump and filter

A plunge pool without jets only needs a circulation pump to move the water through the filter. Most builds use something under 1HP. A variable-speed pump costs more upfront but is much cheaper to run. If you add a swim jet, it has its own dedicated pump. The swim jet kit with pump uses a 4HP 230V pump, and there’s a dual-pump version for a stronger current.

Size the filter for the volume of water and the pump’s flow rate. Oversizing it does no harm and eases the load on the pump. Don’t skimp here. I used a Waterway cartridge filter and I’ve been very happy with it. For bigger plunge pools, a sand filter is worth a look. See sand vs cartridge filters.

Control room

Make it bigger than you think, and give it a drain. Water will escape when you change a filter or service the pump, and the expensive parts are meant to stay dry. I learned that the hard way. I cast a pipe into the floor of mine and removed it once the concrete had set, leaving a hole into the soil below. Some people add a sump pump with a float switch too. See control room design considerations.

Lights

A light is a must, as it lets you use the pool at night and it looks fantastic. On my build, the swimming pool light I chose caused me problems. That’s partly why I launched my own super slim DIY pool light, which suits block and ICF builds. In a pool, lights in the water must run at extra-low voltage (12V). See underwater lighting made simple.

Heating, or keeping it cold

Heating is where a plunge pool is very different from a hot tub, simply because there’s so much more water. (If you run it at hot tub temperatures, the CPSC advises never going above 104°F (40°C).) For my 2,800-litre tub, I used a Balboa spa pack with a 3kW heater. From cold in December, it took about 40 hours to reach 39°C, rising at roughly 0.5°C an hour, faster in summer. Now scale that up to a plunge pool:

Water volume	Energy to raise it 10°C (18°F)	Hours with a 3kW heater (no losses)	Hours with 12kW of heat output
2,800 L (my hot tub)	~33kWh	~11	~3
8,000 L (~2,100 US gal)	~93kWh	~31	~8
13,000 L (~3,400 US gal)	~151kWh	~50	~13

Real heat-up times are longer, because the pool loses heat while it warms. A small spa heater on its own is too slow for most plunge pools. An air source heat pump is the sensible choice today. It typically delivers several kW of heat for every kW of electricity it uses, and many models can cool as well as heat. See how to choose the right air source heat pump. Gas is quicker still if you have a supply. And whatever you choose, a good insulated cover makes the biggest difference to running costs.

For control, I used a Balboa spa pack with WiFi, plus a simple topside panel in case the app played up. Today you’d pair a current spa pack with the Control My Spa WiFi module.

Using your plunge pool as a cold plunge

Lots of people now build a plunge pool partly for cold water immersion. Unheated, an in-ground pool is properly cold for much of the year in the UK and the northern USA. For consistent cold in summer, you’ll need a chiller or a heat pump that can cool.

• Cold water shock is real. The US National Weather Service warns that cold shock can be just as dangerous at 10–15°C (50–60°F) as in near-freezing water, with a gasp reflex and a spike in heart rate and blood pressure. Get in slowly, never plunge alone, and talk to your doctor first if you have a heart condition.
• Keep sanitising and filtering. Cold water is less hospitable to bacteria, but it isn’t sterile.
• Protect the plumbing from frost if the pool is kept cold in winter. Keep water circulating through frosty spells.

A hot tub and cold plunge side by side is a brilliant combination. See how to build a DIY cold plunge pool, cold plunge tub: can you build your own?, Kyle’s cold plunge and hot tub combo and Hot tub and cold plunge: let the build begin.

Electrics

This is the one job to leave to a qualified electrician. It’s dangerous to get wrong and can void your insurance, but you need to know what to ask for.

The cable size depends on the total load, the length of the run and how the cable is installed, so your electrician has to calculate it. Here’s what does apply:

UK

• A dedicated circuit from the consumer unit, with 30mA RCD protection. The RCD type must match what the equipment manufacturer specifies.
• BS 7671 Section 702 (swimming pools) applies. It divides the area around the pool into zones. Only 12V SELV equipment such as lights is allowed in the water, and no sockets are allowed within 2m of the pool edge. Supplementary equipotential bonding of metalwork, including the rebar, is required. The IET says outdoor hot tubs should be treated under Section 702 too, with an isolator outside zone 1, 2m from the edge.
• Armoured (SWA) cable for the outdoor run, buried at a safe depth or fixed securely to a wall. I clipped mine along the garden wall rather than dig a deep trench, and chose armoured cable so I didn’t have to worry about the kids riding their bikes into it.
• It’s notifiable under Part P, so use a registered electrician who can certify it.

USA

• You’ll need a 240V supply. Most US homes already have one via the split-phase service (two 120V legs). Heaters that run on 120V only manage around 1–1.5kW, which is nowhere near enough for a pool.
• NEC Article 680 covers GFCI protection, a disconnect within sight of the equipment (generally at least 5ft from the water), and equipotential bonding. The bonding covers the pool’s rebar, the perimeter surface out to 3ft from the pool, and metal parts nearby, all tied together with solid copper no smaller than 8 AWG. Tie in the rebar bonding before you pour, or it can’t be done. See ground bonding for a hot tub or plunge pool.

Equipment must also match your supply: UK kit is made for 230V/50Hz and US kit for 60Hz. There’s more in A guide to hot tub electrics.

Tiling and finishing

Tiles

Porcelain is the less absorbent choice. Under ANSI A137.1, porcelain tile must have water absorption of 0.5% or less. My large grey ceramic tiles have done fine, but the membrane behind them is what keeps the water in. Having seen hundreds of builds since, I’d choose frost-resistant porcelain or glass mosaic pool tiles. Mosaics follow curves and steps far better than big tiles, and they’re less slippery underfoot.

Adhesive, grout and curing

Don’t just use a “waterproof” shower grout. Use a swimming pool-grade flexible adhesive and grout designed to be permanently underwater. Epoxy grout at the waterline is worth considering. Then leave it to cure for as long as the data sheet says before you fill. Nobody had told me this. I was on a mission to finish in time for Christmas, and my system needed three weeks, which knocked my schedule back. My wife was right when she said it would be awful for a tile to come loose in the first few uses because I was impatient.

Don’t score and snap tiles by hand. A cheap wet diamond tile cutter makes life far easier (wear eye protection). For edges, I used plastic bathroom trim. Metal looks better, but once the pool is full, nobody sees it.

Around the pool

Chlorinated water and grass don’t mix, decking gets slippery (anti-slip coatings help), and in my opinion artificial grass looks rubbish unless you spend a lot. I built a deck and a western red cedar fence, which finishes mine off perfectly. Budget for this separately.

A bit of audio visual

I’ve spent over 15 years in AV, so of course I put a TV and speakers in. Plan the cables in from the start, and use outdoor-rated ethernet. My first indoor-grade run failed within a year, and I suspect something with teeth. Use marine-grade speakers with a volume knob you can reach from the water, because remotes end up at the bottom of the pool after a few drinks. My “outdoor TV” is a cheap 32in set in a home-made splash-proof cabinet with a Perspex front and two small fans to stop it misting up.

Filling, testing and fixing leaks

This was the most nerve-racking and exciting part of my build. A garden hose delivers roughly 1,000 litres an hour, so my tub took about three hours to fill. A 13,000-litre plunge pool will take the best part of a day. Check for any hosepipe ban first.

• Watch every stage as the water reaches the returns and skimmer, then start the pump on low and check every joint. On mine, the one awkward joint dripped, and the pump unions needed a bit of a turn.
• If you’re topping up every week, you have a leak. At first I thought weekly top-ups were just evaporation. They weren’t. Today I top up every couple of months. To check, do a bucket test: put a bucket of pool water on the step, mark both levels, and compare them after 24 hours.

My two leaks were both in the plumbing, which matches what I’ve seen since. Structural leaks are rare, and nine times out of ten the leak is in the pipework. The first was a T-joint on the suction side. A wet-surface plumber’s putty stopped it, but the proper fix is to cut out a bad joint and remake it. The second was my ozone injector, which was held on with jubilee clips. Anything clamped with jubilee clips in a pressurised system will eventually leak, so I cut it out and replaced it with proper pipe and two 90° elbows. There’s more in Help! I’ve a leak.

Water care: chlorine, bromine or salt

You need a sanitiser to kill bacteria, plus pH and alkalinity control. The US CDC recommends free chlorine of at least 1ppm in pools (2ppm if you use stabiliser) and at least 3ppm in hot tubs, with pH between 7.0 and 7.8, and testing at least twice a day when the pool is in use. If you run your plunge pool hot, treat it like a hot tub.

• Chlorine is cheap and the most common choice. Bromine is gentler on sensitive skin and copes better with hot water. See bromine or chlorine?
• Salt chlorination still uses chlorine, just generated on site from salt. It feels softer, but salt is corrosive, so use salt-rated equipment, avoid soft natural stone, and fit a sacrificial zinc anode to protect metal parts.
• UV or ozone can reduce how much chlorine you need, but they don’t replace a residual sanitiser.

For the full routine, see the ultimate guide to balancing chemicals.

Common plunge pool mistakes

• Digging to the water depth and ending up with steps and benches that are too shallow.
• Using a sand and cement mix for the slab instead of reinforced ready-mix concrete.
• Leaving out the hydrostatic relief valve or using a single main drain.
• Relying on additives and PVA instead of a proper pool membrane, or tiling before a flood test.
• Mixing imperial and metric pipe, or bending pipe to avoid joints.
• A control room with no drain and no space to work.
• No safety barrier or lockable cover.

There are more in What I’d change if I built my DIY hot tub again. To see a real plunge pool build, read Ben’s DIY concrete plunge pool in Pennsylvania.

Planning your own plunge pool?

If a standard size fits your garden, my plunge pool / cocktail pool plans give you architectural drawings, plumbing layouts, steps and lounger details, a build guide and videos, in imperial and metric:

• 10ft x 7ft plunge pool plans
• 12ft x 8ft plunge pool plans
• 14ft x 7ft plunge pool plans
• 14ft x 10ft plunge pool plans
• 15ft x 8ft plunge pool plans
• 16ft x 9ft plunge pool plans
• 20ft x 10ft plunge pool plans

Want to swim in it? Add a counter current swim jet to any pool of 14ft (4m) or longer.

If your space is an odd shape, or you want a plunge pool and hot tub combined, start with the free Tub & Pool Designer Pro software. I can then turn your design into architectural CAD and a 3D plumbing design that you can build from or take to your permit office.

FAQs

How deep should a plunge pool be?

Most plunge pools have about 1.2–1.5m (4–5ft) of water, which is enough to stand with your shoulders under. The hole needs to be roughly 350–400mm (14–16in) deeper than the water to allow for the slab, sub-base, waterproofing and tiles.

Do I need a fence around a plunge pool?

In most of the USA, yes. Local codes typically require a barrier at least 48in high with a self-closing, self-latching gate. In the UK there’s no legal requirement for a private pool, but RLSS UK recommends secure fencing at least 4ft high, and a lockable cover is a good extra layer.

Do I need planning permission for a plunge pool in the UK?

Often not. In England, a garden pool is usually permitted development under the outbuildings rules, as long as it isn’t in front of the house and doesn’t take the total covered area over half the garden. Listed buildings, conservation areas and other designated land are exceptions. The electrics still need Part P certification.

Can I use a plunge pool as a cold plunge?

Yes. Leave it unheated, or add a chiller or a heat pump that can cool, and keep sanitising. Take cold water shock seriously: get in slowly, never plunge alone, and check with your doctor if you have a heart condition.

What’s the best way to heat a plunge pool?

For most people, an air source heat pump combined with a good insulated cover. A small electric spa heater is too slow for the volume of water, and gas is fast but more expensive to run.

Building your own plunge pool? Drop your questions in the comments below. I read them all.

Cheers,
Andi

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Thanks - Andi

 

Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Fast forward to 2025, I've helped over 1400+ DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi