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 pollution sanitary sewer overflows. Some cities also have combined sewers, which may discharge untreated sewage during rain storms. Silt (sediment) from sewage discharges also pollutes water bodies. Pathogen discharges may also be caused by poorly managed livestock operations. Contaminants may include organic and inorganic substances. Many of the chemical substances are toxic. Organic water pollutants include: Inorganic water pollutants include: Macroscopic pollution – large visible items polluting the water – may be termed "floatables" in an urban storm water context, or marine debris when found on the open seas, and can include such items as: Thermal pollution is the rise or