Because water is so effective at dissolving substances, even after filtration methods are used, microscopic materials usually end up in water supplies as TDS, some of which can be potentially harmful in high doses. While some may believe that the presence of minerals in the water they consume is a good thing, many realize that the health risk involved with ingesting unwanted TDS in their water is not worth whatever benefits there might be. On the other hand, others, such as hydroponic farmers, for example, may desire the presence of TDS in their water, to make sure that there are enough nutrients being fed to the crops. Everything that consumes, uses or lives in water is affected by TDS, for better or for worse. TDS are commonly found in tap or well water because a combination of leaves, silt, plankton, industrial waste and sewage gets into the water supply, as well as runoff from road salts used during the winter, and from fertilizers and pesticides used in agricultural areas. Lead and copper particles can also get mixed into water supply as the liquid travels through pipes, and water may come into contact with inorganic materials, such as rocks or the air, which can infuse calcium bicarbonate, nitrogen, iron phosphorous and sulfur into water, along with other minerals. Combinations of these materials can form a residue of salts – compounds that contain both a metal and a nonmetal, which, when dissolved in water, usually form ions. Ions consist of cations (positively charged ions) and anions (negatively charged ion). Essentially, the TDS concentration measurement is the sum of the cations and anions found in water.