Water of crystallization degree of hydration can be critical to the resulting chemical properties. For example, anhydrous RhCl is not soluble in water and is relatively useless in organometallic chemistry whereas RhCl•3HO is versatile. Similarly, hydrated AlCl is a poor Lewis acid and thus inactive as a catalyst for Friedel-Crafts reactions. Samples of AlCl must therefore be protected from atmospheric moisture to preclude the formation of hydrates. Crystals of hydrated copper(II) sulfate consist of [Cu(HO)] centers linked to SO ions. Copper is surrounded by six oxygen atoms, provided by two different sulfate groups and four molecules of water. A fifth water resides elsewhere
Water supply and sanitation in Israel of groundwater was first introduced, has shown a constant improvement in the quality of drinking water, with the percentage of violations decreasing from 8.4% in 1989 to 2.1% in 1999. In 2000, the Minister of Health signed an amended version of public health regulations which raise chemical standards for water quality to very stringent standards. Maximum levels for 38 new chemical substances—including pesticides, organic solvents and petroleum products—were set for the first time while existing standards for nitrates, lead, cadmium and zinc were tightened. The salinity of supplied water in Israel varies from very low salinity water (10 mg/l of