Total Dissolved Solids

Total Dissolved Solids (TDS) is the total weight of soluble material in the water (measured in mg/l).

The TDS level will rarely be an issue in a domestic pool where regular backwashing of the sand filter automatically dilutes the pool water by about 5% every time the filter is backwashed.

However in extreme cases a high TDS level can erode the grout in tiled pools, corode stainless steel elements in and around the pool, reduce the effectiveness of UV cells and substantially decrease the transparency of the pool water.

One of the primary solubles is calcium carbonate that produces "Hardness" in the water which is incredibly important. See Water Hardness Effects for more information.

Disinfectants and other pool chemicals such as the acids required for pH correction as well as the pollution from bathers all contribute to a steady buildup of TDS in a swimming pool.

TDS can be monitored by comparing it by testing the pool water and mains water. If the TDS of the pool water is more than 1000 mg/l above the feed mains water the pool water should be diluted by emptying and refilling until the TDS is much closer to the mains water level.

Salt water chlorination systems will always increase the TDS level in a pool to very high levels and is on of the reasons why Bluepools never used them. They should only be used in very soft water areas where the lack of calcium carbonate reduces the TDS level substantially. See Salt Water Chlorination for more information.