Reliable supply of safe drinking water is essential for everyday life. In many places, drinking water is drawn from multiple sources such as river and chemically-treated wastewater system which possibly contain pollutants or contaminants unsafe for health. In modern world where agricultural practices and manufacturing processes in industrial facilities use potentially dangerous substances, water supply contamination is rapidly becoming a threat to public health. Some hazards commonly found in unfiltered drinking water are as follows.
Natural bodies of water including lakes, groundwater, and rivers normally contain both nutrients and microorganisms such as viruses and bacteria. Fortunately, those microorganisms are not pathogenic and they do not cause diseases in humans. However, it is not uncommon that wastes from residential buildings and wild animals also flow in those bodies of water. Sewage is sometimes discharged into those waters as well. Natural aerosol droplets for examples fogs and geyser steams can contain dangerous pollutants too.
Arsenic is distributed in small quantities in waters all around the world. According to World health Organization (WHO) guideline, 10 parts per billion is considered safe, but some countries lower the standard to 50 parts per billion due to the difficulties of removing arsenic from water supply facilities.
One of the most famous hazards in drinking water is lead. It is a heavy metal that can leach from plumbing fixtures and lead pipes, especially in an area where water is highly corrosive. Common symptoms of lead ingestion include behavioral and neurological problems in children and adverse health effects in adults. Cases of lead contamination are common in a city with decades-old water supply systems. Surprisingly enough, even brand new plumbing system with brass fixtures and faucets can also contain significant amounts of lead. Relatively new houses (20 years old or younger) are not necessarily lead-free either.
Unlike lead which comes from metal materials, fluoride is naturally occurring component of water. At recommended value (WHO guideline is 1.5 milligrams per liter), fluoride offers the benefits of reducing tooth decay. When the amount exceeds the recommended level, fluoride becomes a dangerous substance which can cause severe skeletal effects and tooth enamel discoloration. The maximum threshold for safe amount is about 14 milligrams per day, both from water and other sources.
In a document published by Natural Resources Defense Council (NRDC), the Associated Press reported in March 2008 that pharmaceutical residues had been found in drinking water of 24 major metropolitan areas across the U.S. In total, the contaminated water supply was used by at least 41 million people. There were at least three types of drugs found including antibiotics, mood stabilizers, and anticonvulsants. Between 1999 and 2000, the U.S. Geological Survey took samples from 139 streams in 30 states and identified both pharmaceutical residues and organic wastewater contaminants in 80% of the sampled sites.