Are Chemicals Used In A Swimming Pool Safe?

by Lucy Bell-Young

When someone says ‘swimming pool,’ one of the first things that springs to mind is that pungent, inescapable smell of chlorine. Chemicals like chlorine are commonly used in swimming pools to disinfect and clean the water so that it’s safe for us to go for a dip without worrying about any side effects. But many people are still concerned about the safety of the chemicals in their local pools, so in this article we’ll seek to look at the chemistry behind whether or not these concerns are valid. 

Are Chemicals Used In A Swimming Pool Safe?
Chemicals are added to pools in order to kill bacteria and maintain a safe alkaline pH

What Chemicals Are Needed For A Pool?

While many people worry that the chemicals added to swimming pools are dangerous, the real danger is actually the pathogens that are present in the water. 

Many types of bacteria and viruses are introduced to pools by bathers, who unknowingly contaminate the water with bodily fluids and shedding skin. If the resulting pathogens aren’t dealt with, they’ll multiply extraordinarily quickly and spread to pool users. In the worst case scenario, this can lead to a variety of illnesses, from skin diseases and diarrhoea to hepatitis and salmonella. 

Sounds gross, right? Well, that’s exactly why chemicals are needed for swimming pools. Without chemicals, microorganisms introduced into a pool by users could be very harmful. That said, the core aim of chemicals used in pools is to disinfect the water and maintain a safe alkaline pH. 

Chlorine And Bromine

Although there are various types of chemicals that can be used as disinfectants, the most common chemicals used in swimming pools are chlorine and bromine. These chemicals can be added to pool water in a few ways, most commonly by:

  • Dissolving granular chlorine, like calcium hypochlorite, in a bucket and distributing it into the pool water
  • Dissolving bromine tablets using a chemical feeder is another common sanitisation method for swimming pools
  • Pouring liquid chlorine, like sodium hypochlorite, around the edges of the pool, ensuring that you use the correct dose 

One method of pool sanitisation that is not recommended, however, is adding chlorine or bromine gas directly to the water. This is dangerous because it results in a violent chemical reaction, and is also dangerous to inhale. 

With granular or liquid forms of these chemicals, the ions have already dissolved in the water at low concentrations, and pose no threat to pool users. This method is also a lot easier and more cost-effective. One of the most common granular forms of chlorine that’s used to disinfect pools is calcium hypochlorite, a reactive compound of chlorine gas and calcium hydroxide. 

Chemical products and tools for the maintenance of the pool
Chlorine and bromine are the most common chemicals used to clean pools. They can be added as granules, tablets or liquids

Calcium Hypochlorite

Calcium hypochlorite is the active ingredient in most water disinfectants. It’s also the active ingredient in laundry bleach products. While this chemical is also called chlorine powder, it shouldn’t be confused with elemental chlorine, which is a highly reactive gas. 

Calcium hypochlorite has one calcium atom, two chlorine atoms and two oxygen atoms, all of which are ionically bonded to form a molecule. This can be expressed by its chemical formula: Ca(ClO)2

Hypobromous Acid

The other most common chemical disinfectant used in swimming pools is hypobromous acid. This is a weak and relatively unstable acid that can kill a wide range of microorganisms. It also helps prevent the growth of algae on swimming pool tiles.

Each molecule of this acid has one hydrogen atom, one oxygen atom and one bromine atom. This is why it’s chemical formula is HOBr.

What Concentrations Of Disinfectant Are Added To Swimming Pools?

When chlorinating a pool, chlorine and bromine are added in low concentrations, usually between two and three parts per million (ppm). To ensure that you’re using the correct amount of disinfectant, it’s important to calculate the volume of water in the swimming pool and avoid adding too much or little. 

Usually, the volume of a regular, box-shaped swimming pool can easily be calculated by multiplying the depth, width and length. Unfortunately, this simple calculation isn’t applicable to curved and irregularly shaped swimming pools. In these cases, the volume can be estimated according to the cubic metre of water being pumped into the pool. 

How Do Pool Chemicals Work?

Chemical disinfectants in swimming pools are safe for humans because of their low concentrations. In fact, the chemicals used in pools are the same chemicals used to disinfect the tap water. This is because chlorination is an important part of several processes that purify water and make it potable.

Although the chemicals used in swimming pools are only present at relatively low concentrations, they’re very effective at killing microorganisms and preventing the growth of moulds, algae and moss. Chemicals like chlorine and bromine are able to do this because of their ionic forms when they’re dissolved in water. Here, they kill the microorganisms in the water in two ways:

  • Destroying the lipid membranes: During this process, the cell membranes of microorganisms are ruptured by the ions of the chemical disinfectant. As a result, the cytoplasm leaks, and this essential bleeds the microorganism to death.
  • Interrupting enzymes and metabolic processes: Even at low concentrations, the ions in pool chemicals can disrupt the metabolic functions of cells by destroying the enzymes. Doing this prevents microorganisms from reproducing and can also kill them.
Chlorine tablet dispenser floating on the pool surface.
You can use chlorine tablet dispensers to safely and easily clean your swimming pool

How To Check Pool Chemical Levels

If the chlorine or bromine level in a pool goes outside of the ideal two to three ppm, either by dropping too low or spiking too high, it could be detrimental for swimmers. If it’s too low, it would be ineffective at killing pathogens in the water, and this could cause various illnesses to develop. On the other hand, if it’s too high, the chemicals could irritate the skin, eyes and mucous membranes in the nose.

This means that it’s crucial to regularly check the levels of chemical disinfectants in a pool. Maintaining their concentrations at optimal levels will ensure the quality of the pool water and the safety of pool users. There are two ways of checking the level of pool chemicals, namely the strip method and the kit method:

  • Strip method: This is where multi-coloured strips are used to estimate the level of chemicals in the water. The strips provide estimates based on the colour change in the strips.
  • Kit method: This is more accurate and precise but is expensive and cumbersome to do. It works by performing a chemical analysis of the water, thus detecting the levels of chemicals.

How To Add Chemicals To A Pool Safely

Adding chemicals to a pool can cause skin irritation or irritation of the mucous linings in your throat and nose. Therefore, the first consideration you have to make when chlorinating a pool is safety. For example, always make sure to wear the relevant PPE, such as gloves, face masks and goggles.

Proceeding with caution, the next step is to measure the level of chemicals in the water. You can do this using either a strip test or kit test, as we mentioned above. After calculating the volume of water in the pool, add the appropriate amount of granulated chlorine, liquid chlorine or bromine tablets to the swimming pool. Ideally, chemicals like these should be added around the perimeter of the water so that it can distribute evenly throughout the whole pool. 

Liquid test kit of swimming pool pH
Either strip tests or liquid tests can be conducted to check the levels of chemicals in a pool

Where To Buy Pool Chemicals

You can purchase swimming pool chemicals from hardware stores, swimming pool supply stores and even online shops. Once you’ve chosen the right chemicals to use, store them in a secure and safe location according to their safety information. It’s important to make sure they’re well out of reach of children and animals, as chlorine and bromine products are extremely hazardous.


The blog on and everything published on it is provided as an information resource only. The blog, its authors and affiliates accept no responsibility for any accident, injury or damage caused in part or directly from following the information provided on this website. We do not recommend using any chemical without first consulting the Material Safety Data Sheet which can be obtained from the manufacturer and following the safety advice and precautions on the product label. If you are in any doubt about health and safety issues please consult the Health & Safety Executive (HSE).