Sources of Pollution in Swimming Pools

Legionella Bacteria under microscope. Legionella mis a source of biological pollution in swimming pools.

Sources of pollution in swimming pools can be grouped into three main categories: physical, chemical and biological.

Physical Pollution

Physical pollution is made up of contaminants that do not dissolve in the water:

  • Dirt
  • Grit
  • Sand
  • Plasters

Lighter physical pollution will float on the surface of the water, where it can be removed via the following methods:

  • Netting – using a long-handled pole with net attachment
  • Scooping – using a long-handled pole with scoop attachment
  • Skimming – the top layer of pool water is removed via the surface-water-draw-off-system (either scum trough, skimmer basket, or deck-level)

Heavier physical pollution will sink to the bottom of the pool and will settle on the bottom, where is can be removed either by sweeping it towards the pool outlets, or vacuuming the bottom of the pool (either manually, or with an automated pool vac).

Any smaller physical pollution that gets past the defences mentioned above will be transported via the circulation system to the plant room, where it will be removed via the filtration system.

Chemical Pollution

Chemical pollution refers to all chemicals that are dissolved or suspended in the swimming pool water. There are a large number of different chemicals that are introduced into the water, either deliberately as part of the treatment regime, or incidentally due to the nature of the source water or via transfer from bather’s bodies. Some examples:

  • Disinfectant, chlorine
  • Disinfectant by-products
  • pH correctant, acid
  • pH buffer, Sodium bicarbonate
  • Calcium harness increaser, Calcium chloride
  • Calcium minerals, hard water
  • Cosmetics, de-odorants
  • Urine
  • Sweat
  • Mucus

It is worth noting that much of the chemical pollution is caused by the addition of treatment chemicals (chlorine, pH correctant etc.) and that the rate of addition of these chemicals is often directly proportional to the addition of chemical (and other) pollution introduced by bathers. The key message here is that the importance of embedding a culture of pre-swim showering cannot be under-estimated.

Biological Pollution

Biological pollution is any pollution that is ‘alive’. Examples below:

Biological pollution is particularly hazardous to bathers as it can cause a number of infectious diseases, some of which can be fatal. It is introduced into the swimming pool water in a number of ways. A few examples are given below:

  • On bathers bodies (skin)
  • Faecal matter
  • Blood
  • Mucus
  • Via the source water
  • On the bottom of outdoor footwear
  • Canoes/scuba gear which has not been cleaned

Biological pollution needs to be dealt with via a process of disinfection and filtration. The most common way of disinfecting swimming pool water in the UK is by the addition of a chlorine-based disinfectant to the pool water circulation system. Fortunately, chlorine kills most (but not all) types of biological pollution.

So that’s the three categories of pollution in swimming pools. Implement systems for dealing with each category and you should be able to maintain a clean, healthy and safe pool.