The EPA advises a maximum contamination level (MCL) of 500mg/liter (500 parts per million (ppm)) for TDS. Numerous water supplies exceed this level. When TDS levels exceed 1000mg/L it is generally considered unfit for human consumption. A high level of TDS is an indicator of potential concerns, and warrants further investigation. Most often, high levels of TDS are caused by the presence of potassium, chlorides and sodium. These ions have little or no short-term effects, but toxic ions (lead arsenic, cadmium, nitrate and others) may also be dissolved in the water.  Below are some of the reasons why it is helpful to constantly test for TDS: Taste/HealthHigh TDS results in undesirable taste which could be salty, bitter, or metallic. It could also indicate the presence of toxic minerals. The EPA's recommended maximum of TDS in water is 500mg/L (500ppm). Filter performanceTest your water to make sure the filter system has a high rejection rate and know when to change your filter (or membrane) cartridges. HardnessHigh TDS indicates Hard water, which causes scale buildup in pipes and valves, inhibiting performance. AquacultureA constant level of minerals is necessary for aquatic life. The water in an aquarium should have the same levels of TDS and pH as the fish and reef's original habitat. HydroponicsTDS is the best measurement of the nutrient concentration in a hydroponics' solution. Pools and SpasTDS levels must be monitored to prevent maintenance problems. Commercial/IndustrialHigh TDS levels could impede the functions of certain applications.