Hot Tub Total Dissolved Solids: When to Drain

What total dissolved solids means

Total dissolved solids, or TDS, is a term you will see on water check strips and in hot tub care guides. It measures the combined amount of all substances dissolved in the water. These substances include minerals from your fill water, residue from body oils and lotions, and byproducts created when sanitizers break down contaminants.

Think of it like a glass of water with sugar stirred in. The sugar dissolves and you cannot see it, but it is still there. In a hot tub, the water holds more and more dissolved material as people use it. The water can look clear even when TDS is high, which is why regular checks matter.

Why TDS matters for your hot tub

High TDS affects how well your sanitizer works. When there are too many dissolved solids, the water becomes saturated, and the sanitizer has a harder time doing its job. You might notice that you need to add more chemicals to keep the water clear, or that the water feels different on your skin.

The CDC notes that proper water treatment is important for preventing swimming-related illnesses. While the CDC does not give a specific TDS number, it emphasizes following manufacturer instructions for water treatment and replacement. Keeping TDS in check is part of keeping the water safe and pleasant.

If TDS gets too high, the water can become cloudy, and you may see a film on the surface or scale on the tub walls. These are signs that a drain and refill is due. For a broader look at choosing a hot tub that's right for you, see our best hot tub guide.

When to drain and refill

The most common guideline is to drain and refill your hot tub when TDS reaches about 1,500 to 2,000 parts per million (ppm). This range is widely cited in hot tub care literature, but you should always follow the specific recommendation in your hot tub manual.

Your water check kit will have a TDS reading. If the reading is in the high range or the color on the strip matches the 'replace water' indicator, it is time to drain. Some hot tubs have a built-in TDS sensor that will alert you when the water needs changing.

A simple rule of thumb is to drain and refill every three to four months with regular use. However, if you use the hot tub heavily, you may need to do it more often. The water's appearance and smell are also clues: if it looks dull or smells off, a drain is likely needed. For step-by-step guidance on the process, see our drain and refill article. If you have an inflatable model, the drain valve is often simpler; check our best inflatable hot tub guide for models with easy draining.

How to check TDS

You can check TDS with a water check strip or a digital meter. Strips are simple: dip the strip in the water, wait for the color to develop, and compare it to the chart on the bottle. Digital meters give a numeric reading and are more precise.

Follow the instructions that come with your kit. The CDC recommends checking your hot tub water regularly and adjusting chemical levels as needed. For specific guidance on TDS and water replacement, refer to your hot tub's owner's manual.

If you are unsure about your results, a local pool and spa professional can check your water and advise on next steps. They can also help you understand what your TDS reading means for your specific hot tub. For a plug-and-play model, some have built-in water care features that make checking easier; see our best plug and play hot tub guide. You can also look for models with a heater that helps maintain consistent water conditions, as covered in our best hot tub with heater guide.

What TDS does not tell you

TDS is one part of water care, but it does not tell you everything. It does not measure the levels of sanitizer, pH, or alkalinity. You still need to check those separately and keep them in the ranges recommended by your hot tub manual.

High TDS does not necessarily mean the water is unsafe. It means the water is less effective at holding sanitizer, which can lead to other problems. The CDC advises that properly treated water with correct chlorine or bromine levels and pH is less likely to spread germs.

TDS also does not tell you about the presence of specific contaminants. If you suspect the water has been contaminated, the CDC has guidelines for cleaning and decontaminating your hot tub. Always follow those procedures if there has been an incident.

Draining your hot tub

When it is time to drain, follow the instructions in your hot tub manual. Most hot tubs have a drain valve or a pump that can be used to empty the water. Some inflatable models can be drained by simply opening the valve and letting gravity do the work.

After draining, clean the tub surfaces according to the manufacturer's recommendations. Then refill with fresh water. The CDC notes that you should follow the manufacturer's instructions for water treatment and replacement.

If you are unsure about how to drain your specific model, consult the manual or contact the manufacturer. A local professional can also help if you prefer not to do it yourself.

What to pick for your situation

Questions

What is total dissolved solids in a hot tub?

Total dissolved solids (TDS) is the measure of all dissolved substances in the water, including minerals, body oils, and chemical byproducts. High TDS can make it harder for sanitizers to work.

What TDS level requires a drain?

The general guideline is to drain when TDS reaches 1,500 to 2,000 ppm, but always follow the recommendation in your hot tub manual.

How often should I drain my hot tub?

A common rule of thumb is every three to four months with regular use. Heavy use may require more frequent draining.

Can I lower TDS without draining?

No, draining and refilling is the only way to lower TDS. Adding more chemicals will not reduce dissolved solids.

Does TDS affect water clarity?

Yes, high TDS can cause cloudy water and a film on the surface. It can also make the water feel different.

Where can I find official guidance on hot tub water care?

The CDC provides general guidelines for healthy swimming and hot tub use. Always follow your hot tub manufacturer's instructions for water treatment and replacement.