Why is My Hot Tub Losing Water Overnight? (How to Find Leaks)

Discovering that your hot tub is losing water can be shocking. What’s causing it? Is it easy to fix? Do I need to call a plumber? Here are the top solutions if your hot tub is losing water overnight.

Hot tub leaks often come from worn rubber gaskets at the union fittings on either side of the heater and the pump. First, cut off the power before doing any checks. Then, close the gate valves to stop the water from flowing, then remove the union fitting to check for worn gaskets.

But small leaks can be addressed with a product like Fix-a-leak by Marlig.

But there’s a lot more to learn. In this article, we’ll find out why hot tubs drain overnight and how often you should top off water in a hot tub. But we’ll also check out whether hot tub sealers work.

Let’s get started.

losing water overnight lg

Why did my hot tub drain overnight?

If a hot tub drained completely overnight or you’re seeing excessive water loss, there is most likely a cracked PVC pipe somewhere under the hot tub. Remove the panels and look where the most water has puddled on the ground, or look for an active drip or obvious crack.

Leaks at the jets or a worn rubber gasket wouldn’t cause it to drain completely overnight. So, the good news is this should be big enough and obvious enough to be easily spotted once the panels are removed.

Let’s take a closer look at the potential causes.

Plumbing leak

A cracked PVC pipe will be obvious IF it’s not embedded in the spray-on foam typically applied under the hot tub’s shell.

Assuming you can see it, follow these steps to fix it:

  1. Ensure the water is fully drained and power is off.
  2. Cut out on either side of the cracked PVC pipe with a hacksaw.
  3. If possible, replace it with a new PVC pipe of the same size and glue it into place.
  4. However, sometimes that is not easily done. In that case, it is possible to put what’s called a “PVC Flexible Coupling with Stainless Steel Clamps” on either side of the new piece and then fully tighten. I’ve done this myself, and it does work fine.
    CLICK HERE to see what I’m talking about on the Home Depot website. Just make sure to get the right diameter for your pipe.

The other parts that could be responsible are those that use seals and gaskets, such as the heater, pressure switches, and gate valves. The pipe unions, elbows, connections, and tees.

Leaky hot tub jet

Jets and nozzles have their own connections and fittings too, and could be one of the reasons for the drain, especially if the drop in the water is restricted to a particular level.

In that case, the jet directly above the water line should be examined.

Cracked hot tub shell

It’s rarely the case that a crack in the spa shell would lead to large leaks, especially if your hot tub shell is a modern model made of acrylic.

But it happens. So, after checking the aforementioned parts, that could be the reason. You may carefully run your finger over the shell to find out if there are cracks.

Luckily, this product on Amazon works great for patching cracks and holes in the hot tub’s acrylic shell! I’ve used it also, and it works great.

So, what can you do after discovering your hot tub is losing water?

That’s what I explored in a recent article I published. I started it off by looking at what causes a hot tub to leak and how to find a leak in a hot tub. But I also revealed why a hot tub could be leaking from the bottom.

Just click the link to read it on my site.

How often should you have to top off the water in a hot tub?

As a general rule, a hot tub will lose 1-2 inches per month and can be topped off about once per month. However, the water temperature and the temperature outside can both affect the evaporation rate.

So, if you’re seeing a significantly larger drop than that, you probably have a leak.

But if not, simply run the hose to the tub and fill it until the water reaches the desired level. Then check the water chemistry and adjust until the right balance is attained.

This has to be done because hot tub water evaporates over time.

Water naturally escapes through swimsuits and some splashes out with use. If it’s not topped off regularly, the hot tub would eventually run out of water! But too much water loss clearly indicates a leak.

I fill mine with a garden hose to the right level, treat it with the appropriate chemicals and test it with my test strips to ensure they’re properly balanced.

Suppose you’re in the market for a used hot tub, what are the things to look for?

In a recent article, I considered whether it’s a good idea to buy a used hot tub and what questions you should ask when buying one. But I also shared info on how to move a used hot tub after purchase.

Just click the link to read it on my site.

Do hot tub leak sealers work?

Hot tub leak detection products such as Fix-a-leak work very well on small leaks or cracks that are up to 1/8 inch in diameter. So, it won’t work for a cracked PVC pipe.

CLICK HERE to check it out on Amazon.

Marlig Fix-a-leak works because it is heavier than water. And there’s no draining before or after you use it! So, it sinks to the weakest place in the hot tub, where the leak is. There’s no need to empty the hot tub before using it.

Simply remove the filter and pour it in and wait for 24-72 hours before using the hot tub.

In my experience of using other leak products, Fix-a-leak by Marlig is the best, and I’ve used it several times. Don’t, however, use it if the outside air temp is below 40° F.

About 48 hours after you’ve applied it, you can replace the filters and adjust the water chemistry as needed, and you’re good to go. It’s ideal for small leaks. If you have giant cracks in your PVC pipes, you’ll have to consider other solutions. It’s got well over 2,000 reviews on Amazon, and almost all of them are 5 stars.

CLICK HERE to check it out on Amazon.

Why does my spa drain when the pump is off?

The most common reason for a hot tub leaking only when the pump is off is a worn rubber gasket on either side of the pump’s union fittings. With the circulation pump on, the suction likely prevents most of the water from leaking. So the amount of water leaking may be greater with the pump off.

Luckily replacing those rubber gaskets is easy, and, in most cases, you won’t need to drain the tub.

Just follow these steps:

  1. Turn off power to the spa at the disconnect.
  2. Close the gate valves on either side of the pump and heater (these are rectangular-shaped PVC parts with a chrome handle protruding from the top; closed the prevent water from the hot tub from flowing.)
  3. With a large wrench or curved vice grips, unscrew the union fittings on either side of the pump. In some cases, the fitting is in 2 pieces with 2 Phillips screws connecting them. Remove the screws to separate the 2 pieces.
  4. Inside will be 1 rubber gasket. Inspect it for any signs of wear or an actual tear.
  5. Replace them if worn or torn. They are likely under $3.00 at your local hardware store. Take the old gasket with you for a perfect match.

Other possible causes your spa drains when the hot tub’s pumps are off are issues with a check valve, spa return line check valves, diverter valves, and valve actuators.

Let’s check them out.

Gate valve

A gate valve prevents water from flowing in both directions. If it is working well, it prevents water from the spa from draining off.

But if one of its parts is bad or the whole valve is defective, it won’t be able to stop water from draining when the pump is off.

Depending on the model of your gate valve, you may be able to replace the part that’s faulty, or you may have to replace the whole valve.

Spa return line check valves

These are smaller check valves that bring water back to the spa. Over time, chlorinated water could corrode its metal parts. If that’s the case, they need to be unthreaded and replaced.

Diverter valves

As their name suggests, they are for controlling the direction of the water flow. They have gaskets and seals that could go bad. The diverter assembly has a gasket that seals water flow from which side you have in the off position.

Valve actuators

Some diverter valves have actuators mounted on them.

These automatically rotate or close certain ports on the valves. But there are times they get stuck on the “on” position, allowing water to drain from that line. Fortunately, valve actuators can be easily replaced.

Is there a drain plug on a hot tub?

A hot tub drain plug is typically located behind one of the removable panels and may be at one of the corners. It usually has a removable cap and is designed to have a garden hose connect to it for easy draining. It will pull out to drain and can be pushed back in to stop the flow of water.

Some hot tub models come equipped with two drain plugs. One is the primary drain plug; the other is the auxiliary drain plug. The former is used for draining the hot tub, while the latter is for bleeding the internal lines.

But how do you actually drain the water?

It’s a fairly simple process. Let’s check it out. First off, you’ll need a garden hose, submersible pump, wet/dry vacuum, and clean rags.

If the drain plug is located just above the drain, simply open it to allow the water to flow into the drain. But if it’s a bit far from the drain, attach a garden hose to the drain plug, then place the other end above the drain, and open the valve.

What if the drain or sewer is located uphill to your hot tub? You’ll need a submersible pump to ensure that the water is drained off.

Depending on the size of your hot tub, this could take up to an hour or two. Even after you’ve drained the tub, there could still be remnants of water left at the bottom.

A wet/dry vacuum would help, but if you don’t have one, you could use your hand or a brush to shift the water toward the interior drain. Then, you could use clean rags to wipe down the interior of the tub to ensure the water has been drained completely.

But if you have one, a submersible pump is ideal because it’s a lot faster. But you want to keep an eye on it to ensure that it’s only drawing in water. It could overheat if it starts drawing in the air.

Hot tub losing water troubleshooting tips

Some hot tub troubleshooting tips when losing water include:

  • Remove the panels on the hot tub to look for signs of water pooling on the ground
  • Then look to see what is directly above the water
  • Look for signs of leaking around the pump and heater connectors
  • Look for any fiberglass insulation that appears wet
  • With the panels off, turn on the jets and see if that creates a noticeable flow of water (in which case a jet may be loose or cracked).

If you had to get started by checking only two places, I’d suggest you check the union fittings on either side of the heater and the pump. Worn rubber gaskets, as I addressed above, wear out or break easily but can be quickly replaced.

The first thing before you get started checking these different parts is to cut off the power to the hot tub.

Then, remove the panels on the side of the tub and look at the spot where the water is dripping or pooling the most. I know one of the tips I listed called for running the jets, so turn it back on for that step.

Now, let’s check out some of the most common culprits.

The Pump

The pump is the first place to check if you suspect that your hot tub is leaking. Check under it to see if there’s leaking water.

The Union Fittings

The union fittings are found around the heater and the pump.

They typically come in two pieces. They screw into each other and are designed to screw onto the opposite fitting. Over time they can become loosened. If that’s what you found out, simply tighten them by hand. Do not use a wrench to tighten them, as this can cause damage.

The Heater

You have to check the entire heat assembly manifold for a leak. That’s a fancy way of referring to a long silver tube that’s usually located on the underside of your control box.

The heater has many parts, and each one could be the culprit. So, they have to be checked. The parts include the heating element, thermostat, pressure switch, and sensors.

If there are leaking parts in the heater, they would need to be replaced. One of the common leaks occurs with the pipe’s union fittings, a result of degraded gaskets and O-rings, which need to be replaced.

Curious about how long an outdoor hot tub lasts?

That’s the theme of a recent article I published. In it, I shared how long hot tubs last and how long should a hot tub pump last. But I also shared how long should a hot tub heater last.

Just click the link to read it on my site.

When is hot tub water loss normal?

Normal evaporation occurs as a natural process when the hot tub is exposed to air and heat.

Factors such as temperature, humidity, and usage frequency can influence the rate of evaporation. Generally, a quarter to half an inch of water loss per week is considered normal.

To determine if the water loss is due to evaporation or a leak, you can perform a simple test.

Fill the hot tub to its normal level and mark the waterline. Then, turn off all jets and ensure the cover is securely in place. Check the water level after 24-48 hours. If the water loss is within the expected range, it is likely due to evaporation. However, if the water level has significantly dropped below the marked line, there may be a leak that requires attention.

If you see inches of water missing, it’s important to locate and address the leak promptly.

Inspect the hot tub for any visible signs of leakage, such as wet areas, dripping pipes, or loose fittings. You can also conduct a dye test by adding a few drops of food coloring to the water near suspected areas and observing if the color appears outside the hot tub.

In some cases, minor leaks can be repaired using hot tub sealants or patches specific to your tub’s material. However, for more significant leaks, it’s recommended to consult a professional hot tub technician for proper diagnosis and repair.

Regular maintenance practices like checking for leaks, ensuring proper seals, and keeping the hot tub cover in good condition can help minimize water loss and potential damage. By understanding the difference between normal evaporation and a leak, you can enjoy your hot tub worry-free and maintain its water level effectively.


Leaks are inevitable for hot tub owners.

In conclusion, if you find your hot tub losing water overnight, it’s important to investigate the cause and take appropriate action.

While some low water levels can be attributed to normal evaporation, excessive or sudden water loss may indicate a leak that needs to be addressed. Conducting simple tests, such as the water level mark test and dye test, can help determine the source of the problem.

Promptly addressing leaks and maintaining regular hot tub maintenance can help prevent further water loss and potential damage. By staying vigilant and taking necessary measures, you can ensure that your hot tub continues to provide a relaxing and enjoyable experience for years to come.

Photo that requires attribution:

101/365: Spa repair. by David Mulder is licensed under CC2.0 and was cropped, edited, and had a text overlay added.

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Jeff Campbell