How Long Can Water Sit in a Pool Without Chlorine?

How Long Can Water Sit in a Pool Without Chlorine

A pool requires constant maintenance in order for the water to be safe to swim in. However, let’s be honest: it’s kind of a pain in the butt maintaining a pool. It’s exhausting to test the water, add a bunch of chemicals, test the water again, every few days, just to keep the water chemistry balanced.

Besides, some people really dislike the side effects that chlorine – the primary disinfecting chemical – causes: irritated skin, red eyes, dried hair, the “chlorine” smell. It makes one wonder if, perhaps, one could simply not add chlorine to their pool. How long can water sit in a pool without chlorine and still be safe to swim in?

How long water can sit in a pool without chlorine depends on numerous factors, including air temperature, humidity, exposure to sunlight, amount of rainfall, how often the pool is used, and if external contaminants are introduced. If you decide to stop treating a pool with chemicals, it only takes 24-48 hours before you can see algae and fungal growth. Within a couple of weeks, it can start to resemble a pond, and any longer than that, a cesspool.

Keep reading on to learn what you’re exposing yourself, your family, your guests, and your pool to by letting water sit in the pool without chlorine.

How long can you leave water out?

If you’ve just filled a kiddie pool with fresh water and your kids played in it for about five minutes before losing interest, it’d be a waste to just dump it all out. But you also don’t feel like adding chemicals, so the water is not actively being sanitized. How long can you leave it out for so you don’t waste a bunch of water?

This is hard to answer because it can change wildly depending on what kind of bacteria have made it into the pool. Generally, the upper limit is thought to be around 24 hours.

However, what happens if, within the first five minutes, someone decides to go number one in the pool? At least in a chlorinated pool, you can rest assured that the chlorine will deal with the urine, but in an untreated pool, you or your family will be swimming in pee the whole time.

Also, if the pool guests don’t shower before entering the pool, they may introduce bacteria and germs that can be transmitted to the other guests in that very same session.

To assume that the water can be safe to swim in for up to 24 hours is assuming that it remains unaffected by external sources of contamination, and even then, it doesn’t take very long before algae starts to grow.

Should you dump the water out after each use?

Even if you have ensured that the water remains untainted by external contaminants before finally taking a dip in it, without chlorine to keep the water sanitized, you should dump it out immediately after each use.

Obviously this would be extremely wasteful for a large pool, but for a kiddie pool this is a more feasible decision. Kiddie pools are much smaller and you can justify replacing the water more often, as you should.

Some kiddie pool owners leave the water in the kiddie pool overnight with a tarp on, thinking that it can preserve the water. However, a tarp does not prevent the growth of bacteria already in the water, and therefore does not keep the water cleaner for longer.

For larger pools where it would be wasteful to dump the water out, you’re going to need to rely on chemicals to disinfect the water. Unfortunately, there aren’t chemicals that can perfectly substitute chlorine, and often still require some amount of chlorine be added anyways.

Plus, if your goal is to run a chemical-free pool, then your only option is to replace the water after each use. This is highly wasteful and uneconomical, so it is not an ideal option.

What happens if you forgo adding chlorine

Increased risk of infection and illnesses

If you decide to swim in an untreated pool, you are at increased risk of infection due to a water illness. This can result in ear and eye infections, as well as upset stomach and diarrhea.

Water illness is a generic term referring to the kinds of bugs you can pick up from public places like the beach, the water park, and swimming pools. Chances are you or your kids have had it happen to you at least once already, and it can easily happen again.

Your chances of developing a water illness is increased even further if you accidentally swallow the water or swim in water where more than one person has swam in. The infections are often caused by E. coli and cryptosporidium, and they spread easily.

Green algae

You’re used to seeing your water looking clean and pristine, but if you forgo chlorine, your pool will be green and unclean. The dreaded green pool is the result of algae growth, and it can happen in as quickly as 24-48 hours.

While algae is unsightly enough in lakes and oceans, they are less of a threat because they are in an open system. A swimming pool, however, is a closed system, meaning no new water is being introduced, and there are no organisms that are dealing with the bacteria around the algae.

Algae is also not the cause of the problems, but rather the bacteria that feeds on algae will result in your swimming pool becoming a breeding ground for some seriously nasty bacteria like E. coli.

This can eventually progress into white and pink, slimy molds which can clog your pool filtration system and reduce its performance. This results in, unsurprisingly, more bacteria. In other words, a green pool is just the beginning.

Extensive damage to the pool

Aside from the health risks posed by not having chlorine, improper water balance and bacterial buildup can also damage the pool itself.

Not maintaining the water chemistry can cause damage to the pool liner, which will eventually crack. If the pH is too low, the high acidity of the water can cause pitting, etching, and delaminating in fibreglass pools.

Furthermore, metal parts like screws, ladders, light fixtures, and pool cover components are at risk of corrosion due to the acidity. These are all good reasons to test your water frequently to keep the pH, alkalinity, and TDS in balance. You should also clean the skimmer basket to allow for proper circulation.

The bottom line

Just as you wouldn’t keep and reuse the same bathwater, especially if other people have also been in that water, it’s not a good idea to let water sit in a pool without chlorine.

The most obvious issue is how unsanitary the water can quickly become. In approximately 24 hours, you will already notice that the water clarity is decreasing as it starts to show a hint of green. Within a few days, it will be completely covered in green algae.

There is also a concern that people may have peed in it or brought bacteria from outside into the pool. You wouldn’t want to swim in your own filth, and chlorine’s purpose is eliminating the filth so that the water remains pristine and safe to swim in.

Ultimately, without chlorine in the pool, you should be replacing the water after each use so that you can avoid getting infections that may require medical attention.

Photo Credit: Daniel Doyle (CC BY 2.0)