One of the measurements that can be taken on swimming pool water is the Total Dissolved Solids level, or TDS. TDS is a measurement of virtually everything dissolved in the water that is not H2O. This includes such components as salts, minerals (like calcium and magnesium), sulfates, silicates, organic and inorganic materials, tanning lotions and oils, sweat, saliva, urine, soap, deodorant, hair spray, colognes and perfumes, plant pollens, pet wastes, spilled food and softdrinks, dirt, lawn and garden fertilizers, etc. Wow! There is quite a lot of dissolved material in that water that is still clear to the human eye!

As water evaporates from the pool, the TDS increases because the sun only removes distilled (pure) water and leaves all of the dissolved solids behind (like when you leave a glass of water outside to evaporate… the white crust left behind was “dissolved solids”). The “fresh” water you then use to replace the evaporated pure water also contains its share of dissolved solids. Normal evaporation rates are usually up to 1/4″ per day in the winter and 112″ per day in the summer. Therefore the water in the pool is continually getting “harder”, or higher in dissolved solid content.

High TDS can be a problem because they interfere with pH, hamper chlorine’s ability to affect bacteria and algae, create hazy water, contribute to the corrosion of metal piping systems, and promote scale deposition on the plaster and tile.

In swimming pool applications, TDS is normally measured by means of a meter that passes electrical current through the water. Since most anything that is not pure water conducts electricity, and since pure distilled water does not, the amount of electricity that passes through can be read as a level of TDS.

Tap water TDS can range from 300 to 700 parts per million TDS. The average in swimming pools is usually 1000 to 2000 ppm. The National Spa and Pool Institute (NSPD recommends an upper limit of 3000 ppm).

TDS can be lowered through full or partial draining and refilling, through the use of chelating agents, or through special nanofiltration. If you wish to know the TDS level in your pool water, or if you are interested in chelation or nanofiltration, please call us.