Water purification is the removal of contaminants from raw water
to produce drinking water that is pure enough for human
consumption or for industrial use. Substances that are removed
during the process include parasites ( such as Giardia or
Cryptosporidium) , bacteria, algae, viruses, fungi, minerals
(including toxic metals such as Lead, Copper etc.), and man-made
chemical pollutants. Many contaminants can be dangerous—but
depending on the quality standards, others are removed to
improve the water's smell, taste, and appearance. A small amount
of disinfectant is usually intentionally left in the water at
the end of the treatment process to reduce the risk of re-
contamination in the distribution system. Many environmental and
cost considerations affect the location and design of water
purification plants. Groundwater is cheaper to treat, but
aquifers usually have limited output and can take thousands of
years to recharge. Surface water sources should be carefully
monitored for the presence of unusual types or