Total Dissolved Solids (TDS, also called total filterable residue or total dissolved residue) is a measure of the water's content of various dissolved materials. Water with no dissolved solids usually has a flat taste, whereas water with more than 500 mg/l TDS usually has a disagreeably strong taste. Depending on the chemical nature of the dissolved solids, reverse osmosis, or lime soda softening may be used to reduce TDS content.