How to fill a hot tub with water – the correct way!

Filling a hot tub with water might seem like a straightforward task – just turn on the hose, place it in the tub, and wait. However, it’s not quite that simple. If you fill water in your hot tub incorrectly can lead to issues like air locks, which can be a headache to fix.

In this guide, we’ll show you the correct way to fill a hot tub with water, whether it’s a DIY build or a pre-made model. So, let’s dive in and learn how to fill your hot tub the right way!

There are a few key things to keep in mind when filling your hot tub with water.

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There are a few key things to keep in mind when filling your hot tub with water.

Start from the Highest Point

Always start filling your hot tub from the highest point. This reduces the pressure of the water entering the tub and helps prevent air from getting trapped in the system, which can cause air locks.

For plastic shell hot tubs, the highest point is typically the filter. Insert the hose into the filter and begin filling. This method forces the water through the plumbing system, helping to push air out as the water fills the tub.

For DIY hot tubs, the highest point is often directly into the tub itself. However, if your control room (where the pumps are located) is below the waterline, filling directly into the tub can create a large air lock as it forces the air further into the system. 

Top Tip: Run the Jets Briefly

Once the water level has risen above the inward suction drain, briefly turn on the jets for 10-15 seconds. This will help purge any air trapped in the system by forcing water through the jets. 

Be cautious, though – don’t run the pumps dry! Ensure the water level is above the suction drain before turning on the jets, as running them dry for too long can cause the pump to burn out.

If air locks persist, continue running the jets for short intervals as long as the water is above the inward suction drain.

What to Do If You Have a Stubborn Airlock

If you encounter a particularly stubborn air lock, don’t worry – there are ways to resolve it. You can check out my video for everything on hot tub plumbing, but the simplest method is to lower the water level below the jets, leaving it just above the inward suction. Run the system while filling it up again to help remove any remaining air.

If you follow these simple tips when filling in your hot tub, you’ll be sure to avoid an airlock or any other problems!

Top Tip for Post-Fill Chemicals

Regarding water chemistry: Always test the source water before adding any chemicals, as different regions have vastly different water compositions. Use test strips or a digital tester for accuracy.

Start by adjusting total alkalinity first (aim for 100 ppm), as this creates a stable base for pH adjustment. For pH, add incremental amounts of pH increaser or decreaser, waiting 15-20 minutes between additions to get an accurate reading. Once pH and alkalinity are balanced, add your chosen sanitizer (chlorine should be 3-5 ppm, bromine 4-6 ppm).

For hard water areas (above 250 ppm calcium hardness), use a scale prevention product during filling. This is especially important if you notice calcium deposits on your shower heads or faucets at home.

The initial heating process can take 8-24 hours depending on your heater size and starting water temperature, so plan accordingly

Can I Help You?

If I can help you in any way I would love to hear from you. You can get in touch using the form below.

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.

Today, I've helped over 1000 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