TDS are the amount of organic and inorganic compounds dissolved in a given volume of water, such as metals, minerals, salts, and ions; TDS of drinking water are essentially a measure of anything dissolved in water that isn't an H2O molecule. When water comes into contact with soluble material, the material's particles are absorbed into the water, resulting in total dissolved solids. TDS can come from a variety of sources, including municipal water treatment chemicals, natural water springs, road and yard runoff, and even the plumbing system at your house.