Find out about swimming pool water quality

Maintaining high levels of swimming pool water quality is key for ensuring the pool is safe for swimming. If the pool water is left untreated, harmful bacteria such as E.coli, Salmonella and Legionella can accumulate, presenting a serious risk to human health. Water balance can be affected by:

• temperature
• pH
• total alkalinity
• calcium hardness
• total dissolved solids

In order to maintain acceptable quality the following should be maintained:

• pH 7.2 - 7.6
• free chlorine 1.0 - 2.0 mg/l 
• combined chlorine residual should be kept as low as 0.5 mg/l and should be no more than one-third of total chlorine
• total alkalinity 80 - 150 mg/l
• calcium hardness 200 mg/l minimum
• total dissolved solids (TDS) maximum 1000 mg/l above supply water TDS to an absolute maximum of 3000 mg/l (2000 mg/l preferable)
• sulphate 360 mg/l maximum

The Langelier formula, sometimes called the Saturation Index, is used to determine pool water balance. The Saturation Index (SI) = pH + Temperature Factor (TF) + Calcium Hardness Factor (CF) + Total Alkalinity Factor (AF) minus Total Dissolved Solids Factor (TDSF).

The value obtained should fall between 0 and 0.5 and indicates the water is in balance.