Total Dissolved Solids

Also Known As: TDS

Also called TDS, Total Dissolved Solids is the total of all solids dissolved in water, typically metals, minerals and salts. Only the gross volume of TDS is measured, so the specific makeup is not clear. Because these are dissolved, they are completely invisible.

Therefore TDS does not include suspended solids. However, sodium chloride may make up the largest percentage of a pool’s TDS, because it is left behind by soda ash, liquid chlorine and other pool additives, as well as human sweat and urine.

Purified water has TDS of 0 parts per million (ppm), while drinking water typically has a maximum of 500 ppm. A swimming pool should have a maximum of about 1,500 ppm TDS. It is recommended that water be maintained at 1,200 ppm. If levels are higher, the pool water can seem cloudy, have an odor and taste salty. In addition, there is a risk of scaling and stains.

However, levels as high as 4,000 ppm can be present in healthy water, making it challenging to use TDS to assess pool-water balance. Other considerations, including alkalinity, hardness, conditioner, pH and metals, are important factors. Salt-water pools may have TDS levels as high as 32,000 ppm.

Draining the pool is one way to lower TDS. Another is to install desalting equipment. Battery-powered, hand-held testers can accurately test levels of TDS.