Asked by: James Smith, Edinburgh
When studying the effectiveness of swimming pool filtration systems, researchers talk in terms of ‘body fluid analogue’ or BFA. This is a mixture of sweat and urine, plus skin and faeces that represents the average concentration of pollutants from swimmers. Each person adds about 25ml of BFA to the water, 6.3 per cent of which is urea. The concentration of wee in a typical pool is about one part per million. Chlorine added to the water reacts with urea to remove it, but only about 1 per cent per hour is removed this way.