Water in our pools

Lisanud Annegrete 2018/04/07

This is already second post in "Open Data and Data Journalism" series. This time we will look at the data of water samples of the Health Board and we will investigate the quality of water in Estonian swimming pools and water parks.

I have to admit that I do not think of water quality when I’m in the water, especially in pools or water parks.

Stagnant water and high number of people are risks for water quality. The water is monitored daily and at least once a month laboratory tests are carried out. Data is submitted to the Health Board and water sample evaluations are available to everyone (see also).

Is the pool water in good condition? Are national requirements easy to fulfill?

I use the Health Board open data to answer questions. I look into swimming pool water samples taken between January 2016 and June 2017, with 7496 observations about 386 swimming pools and hot tubs.

Unfortunately, every fifth water sample does not meet the requirements. Typically, in one water sample 5-17 indicators are viewed. If the water sample does not meet the requirements, 72% of the cases are due to one bad indicator and 21% due to two bad indicators. In most cases, non-compliant indicators are free or bound chlorine. By the way, chlorine is the most common disinfectant in pool water in Estonia.

75% of the samples remain in the required range of 0.5-1.5 mg/l. If the free chlorine indicator does not meet the requirements, in general, the problem is with too small amount. But rarely - in 2% of cases - this figure is very high (over 2 mg/l).

Free chlorine is part of the chlorine in water that is originally added to water and has a high disinfection capacity to keep the water clean and clear and has not yet reacted with organic substances in water. Free chlorine does not cause skin or eye irritation. 1

Only an upper limit is set for bound chlorine. In a warm pool (above 31 °C), the chloride may be up to 0.5 mg/l, in a cooler pool (up to 31 °C) up to 0.4 mg/l. In every fifth water sample, too much chlorine is present.

Bounded chlorine is a part of chlorine that has reacted with ammonium compounds in water, which in turn occurs, for example, from sweat, urine, dead skin cells, bacteria, sunblock, and the like. Bound chlorine is also called chloramine. This is what causes the so-called chlorine smell that is thought to be due to excess chlorine. Chloramine causes irritation of eyes, skin and respiratory tract. The greater the pool load and water pollution, and the less purified and fresh water is supplied, the greater the chlorine content. 1

The next time you go to enjoy water, see if your pool's water is still in good shape. You can do this here.

The Open Data Portal's content is created as part of the EU structural funds' programme 'Raising Awareness of Information Society' which is financed through the EU Regional Development Fund. Project activities are carried out by the Open Knowledge Estonia NGO.


1 http://terviseamet.ee/keskkonnatervis/vesi/ujulad.html