If your tap water has a clouded appearance, there are several possible causes. If the cloudiness signifies contamination, you can apply one of several treatments to ensure clean and safe drinking water. In some cases, cloudiness occurs in completely pristine drinkable water. To determine your course of action, weigh the circumstances; if you are traveling in developing countries, for example, stay on the safe side by using purification treatments.
Letting It Settle
One of the principal causes of cloudy water in developed countries and well-managed water systems is the completely harmless behavior of air bubbles in the water. All water has some quantity of dissolved air, usually to an unnoticeable degree. However, in some cases tap water comes out of the faucet with somewhat larger, more visible water bubbles, still sufficiently tiny to appear like a general cloudiness. In some cases, the water even has a milky look. When outdoor temperatures drop, there is a large temperature difference between the pipes delivering water and the interior where the water arrives; this change in temperature can aggravate the tendency for "cloudy" air bubbles to form. For example, the water from the Los Angeles aqueduct originally comes from the icy waters of the eastern Sierras; it remains cool until it arrives through home faucets. To remove the cloudiness, simply let the water sit at room temperature for several minutes.
If you have any reason to question the tap water's safety and cleanliness, you can easily disinfect it chemically by adding iodine tablets. Iodine will kill many of the most common parasites found in unclean water, such as cryptosporidium, which commonly causes diarrhea. Keep in mind that some parasites, such as cyclospor or toxoplasma, can still survive disinfection by iodine. When treating cloudy water, it's best to double the recommended dosage of iodine tablets. To make iodine most effective, add it to water at room temperature. If possible, warm any water that is cooler than 41 degrees Fahrenheit before adding any type of treatment.
If letting your water sit at room temperature doesn't remove its cloudiness, you can use basic filters to strain out any sediment. The Federal Emergency Management Agency and Center for Disease Control advise using paper coffee filters or several layers of clean fabric to remove the cloudiness from water. Keep in mind that if there is any risk of contamination in the tap water, filtration alone will not remove any bacteria or parasites. It will simply make the water more transparent, and it is best used in uncertain environments as a secondary measure, following iodine application.