Water is often called the universal solvent because it can dissolve so many other substances.
Hard and Soft Water
Hard water does not lather easily with soap, because of dissolved calcium and magnesium ions.
- Temporary hardness is caused by calcium or magnesium hydrogen carbonate, and can be removed simply by boiling.
- Permanent hardness is caused by other calcium or magnesium salts and cannot be removed by boiling — it requires distillation, washing soda, or an ion exchanger instead.
Spring water, tap water and bottled water are typically hard. Soft water — such as rainwater or distilled water — lathers easily and is preferred for laundry and as laboratory water.
Testing for Water
Anhydrous copper(II) sulphate (white) turns blue in the presence of water; anhydrous cobalt(II) chloride (blue) turns pink in the presence of water. Either can be used as a chemical test to confirm water is present.
Sources of Water
Natural sources include rain, springs, wells, rivers, streams, seas and oceans. Artificial water is water that has been purified, such as tap-borne or distilled water.
Water Pollution
Water pollution is the discharge of harmful substances (pollutants) into water bodies. Common sources include sewage from homes, agricultural runoff of herbicides and pesticides, and industrial waste discharged directly into water or released as gases that are later washed down by rain.
