TDS stands for Total Dissolved Solids In Water. "Dissolved solids" refer to any minerals, salts, metals, cations or anions dissolved in water. This includes anything present in water other than the pure water (H20) molecule and suspended solids. (Suspended solids are any particles/substances that are neither dissolved nor settled in the water, such as wood pulp.)

In general, the total dissolved solids concentration is the sum of the cations (positively charged) and anions (negatively charged) ions in the water. This actually is a conductivity test of available ions in the water, including Ca2+, Na+, K+, Fe2+, Fe3+, HCO3- and ions containing P, S & N. High levels of Na+ is associated with excessive salinity and is found in many minerals. Potassium is incorporated into plant material and is released into water systems when plant matter is decayed or burnt.

Now that we know what TDS is, let's talk about from where Dissolved Solids come from. Some dissolved solids come from organic sources such as leaves, silt, plankton, and industrial waste and sewage. Other sources come from runoff from urban areas, road salts used on street during the winter, and fertilizers and pesticides used on lawns and farms. Dissolved solids also come from inorganic materials such as rocks and air that may contain calcium bicarbonate, nitrogen, iron phosphorous, sulfur, and other minerals. Many of these materials form salts, which are compounds that contain both a metal and a nonmetal. Salts usually dissolve in water forming ions. Water may also pick up metals such as lead or copper as they travel through pipes used to distribute water to consumers.

If you have installed a water filter or a Reverse Osmosis (RO) system or have yet to install, the only way to know if your reverse osmosis RO membrane is performing correctly is TDS. It's a must for all RO system owners. You can compare incoming feed water to treated water. Replace membrane/filter if less than 80% of TDS is being removed. The lower the TDS level in the water, the more efficiently your body's cells actually get hydrated by the water that you drink. The higher the TDS levels in the water, the greater the probability of harmful contaminants that can pose health risks or hinder the absorption of water molecules on the cellular level. 17 PPM of TDS = 1 grain of hardness. Anyone who wants to know about the quality of their water and its hardness, should have one of these TDS Meter Testers. The TDS meter is an excellent means by which you can regularly test your water supply, as well as your water purification system and its performance in cleaning your water. If you notice the TDS level beginning to show an increase in your reverse osmosis or other water purification system, then it is time to change the filters or cartridges.