No water is completely pure. Contaminates, both naturally occurring and manmade, occur at differing levels depending on your location throughout the world.
In the United States, federal and state regulations set standards for the maximum amount of contaminants allowed for water to be considered safe for drinking. Regulated contaminants include a variety of microbes and substances that at certain levels could cause adverse health effects.
Though most treated drinking water is safe for consumption, some contaminants can be introduced into the water after it is treated. One example is water that comes in contact with lead that can leach into water from the pipe systems in older homes.
Other contaminants that are not regulated as potentially harmful, may yet affect water’s aesthetic quality. Higher levels of minerals in hard water may give water a metallic or unpleasant taste as well as odor and cloudy appearance. Substances such as geosmin, produced by algae, can give water an unpleasant taste and odor.
While some regulated contaminants are considered safe for the average person at levels allowed under government regulations, they could pose a hazard for those with weakened immune systems. People with immune systems compromised through illness, chemotherapy or transplant medications should take a closer look at the treatment of the water they drink, whether from their tap or a bottle.
A potentially hazardous contaminant is cryptosporidium, a microscopic parasite that lives in intestines of warm blooded animals including humans and is passed with waste. In healthy people, the parasite can cause illness with symptoms including diarrhea, vomiting, fever and dehydration among others. Cryptosporidium can prove deadly for those with weakened immunity. The parasite is very resistant to chlorine-based disinfectants and boiling is considered the most effective way of killing it.
An emerging category of pollutants includes pharmaceuticals and personal care products. Though scientists have found no evidence of adverse effects on human health, some studies suggest these substances can harm the environment. Research continues on the issue.