You can keep on chucking chemicals into a swimming pool and it’ll stay reasonably clean and sanitised. Hot tubs are different. The water in your hot tub needs to be changed regularly. Here’s what happens if you don’t – and what to do about it.

Why change hot tub water? You’ve seen CSI…

Humans leave all kinds of stuff behind wherever we go. It in a hot tub it floats off into the water, everything from dandruff and miniscule pieces of skin to hairs, sweat, ear wax, foot cheese (and worse), snot… and we’re not even going to go near the toilet side of things. Suffice to say unless you have a bidet your hot tub will turn toxic even sooner.

Add cosmetic products, deodorants, sun cream, moisturises, hair conditioner, food and drink, insect effluvia, dead flies and dust, and anyone in their right mind would be gagging before too long. But there’s more. While sharing a tub with close family is one thing, getting friends and relatives involved is another. Add more guests to the hot tub recipe and things get muckier, faster. And if that alone hasn’t convinced you how important it is to change the water in a hot tub, nothing will! 

You’ve watched CSI, you get the picture. However spotless and squeaky clean you think you are, every time you use your hot tub you will leave bits of you behind in the water.

A hefty dose of chemicals can only do so much 

Chlorine and bromine do a top job at neutralising all this nastiness, they can only do so much. Once the water is saturated with chemicals it stops working. Even if it didn’t, the water is full of invisible dissolved disgustingness, too horrid not to change to a regular schedule. Eventually, if you leave it so long the chlorine or bromine starts to crystallise out, the water feels really gritty and the particles eventually stick to the sides of the tub, like bathing in a sandpaper container. Not nice. 

The hotter it is, the happier the pathogens 

The weather matters, too. The hotter it is, the happier pathogens are and the more they’ll grow and spread. There’s a lot of scientific evidence proving injuries heal faster and are less likely to fester in cold climates where there aren’t as many viruses and bacteria. They just don’t like the cold. In warm weather, even in the UK, anything in the water that can proliferate probably will when the temperatures soar, especially when your hot tub chemicals are out of balance or approaching saturation point. When it’s properly hot some microbes more or less go postal. 

If it looks revolting, it probably is

Looks-wise, the water will steadily get more cloudy and murky until you can’t see the bottom of the hot tub. Grim. There might also be a bio-film (steady now, don’t throw up), a thin layer of oily living stuff building a housing estate for itself on the surface of the water. Even actual green algae. Honestly, you really don’t want to be sitting your ass in something as soupy as that.

If it looks like a duck and quacks like a duck, it’s probably a duck. The same goes for dirty hot tub water. If it looks unhygienic and smells like sh*t it is probably full of it, and sh*t is not good for your health!

So, following a long, complex and nauseating journey, here we are answering the all-important question: how often should you change the water in your hot tub?

How often to change hot tub water

If this diatribe of revoltingness has opened your eyes to hot tub hygiene you can, of course change the water in your hot tub as often as you like bearing in mind the cost of heating a fresh tub full of water from scratch every time. Some people change the water as soon as it looks dirty, others let it go ‘til it’s verging on stinky. According to most hot tub professionals, once a quarter should usually do the trick. On the other hand, like so much in life, it can get complicated. If you’d rather delve into the nerdy detail, here goes.

To tailor your maintenance to the actual conditions, four factors drive your timing. First, as we’ve mentioned, the weather. Sunny or not, if it’s been extra hot you might choose to refill your hot tub more often because of those dratted warmth-loving pathogens. If it’s starting to look scummy, change it.

Second: how much water your hot tub holds, the volume. The more water is in the tub, the more chemicals can dissolve in it before it gets saturated. The bigger your tub, the less often you need to refill it. The information will be in the manual or online but as a guide you’re looking at:

• 200 gallons for a 2 seater
• 250 for a 3 seater
• 300 for a 4 seater hot tub
• 350 for a 5 seater
• 400 for a 6 seater hot tub
• and a mighty 600 gallons for an 8 seat tub

Third: how many people use your hot tub, the bather load. The more people use it, the more frequently it’s used, the more contaminants get into a hot tub and the more frequently you should replace the water.

• Say it takes one of you six months to mucky the water enough to merit a water change. 2 people reduces it to 3 months, 3 to 2 months and with four people using the tub at the same time you’re looking at a water change every six weeks

What if, like most people, sometimes you have a load of people in the tub, other times just the one or two? Simple maths will reveal the average. If most times it’s just two of you, it doesn’t matter if you have more or fewer people now and again. It’ll average out. For infrequent use you could figure out the weekly average and divide it by 7 for the days of the week.

Fourth and last, how you sanitise the hot tub influences how often you refill it. Chlorine and bromine come in granules, tablets, and liquid form, both basically kinds of bleach. Chlorine itself also comes in different types, the most popular being a stabilised granular form called dichlor. Some people use a combo of this and liquid chlorine, not necessary but fair enough when you’re a belt-and-braces sort of person who doesn’t mind sitting in something that smells like a 1970s schoolboys’ changing room.

Should you ever change the water sooner?

As we’ve mentioned there’s no hard and fast rule but sometimes you can’t fix things with chemicals alone. Dog poo and child poo. Biofilm. Bigger than crumb-sized bits of food, and big booze and juice spillages. Some dogs love hot tubbing, and you can imagine what one or more pooches will leave behind. Ugh. Then there’s kids with filthy muddy feet, commonplace when they’re constantly in and out of the tub. If you’re in it for the thrills, this is about as far from a thrilling task as it gets but gird your loins, plaster a smile on your face and revel in the pleasure of knowing that you have kept your hot tub in a hygienic condition and kept those you love from the many horrors of dirty water. Whether you need to go through this process every month or every six, your hot tub parties will be better for it.