In commercial or laboratory preparations, reagent-grade designates chemical substances meeting standards of purity that ensure the scientific precision and reliability of chemical analysis, chemical reactions or physical testing. Purity standards for reagents are set by organizations such as ASTM International or the American Chemical Society. For instance, reagent-quality water must have very low levels of impurities such as sodium and chloride ions, silica, and bacteria, as well as a very high electrical resistivity.  Laboratory products which are less pure, but still useful and economical for undemanding work, may be designated as technical, practical, or crude grade to distinguish them from reagent versions.