Once upon a time, up until about 100 years ago, it was always found that water flowing from natural springs was safe for drinking in its natural state, but in the 21st century even spring water is first scientifically tested before it is recommended or bottled for drinking.

One of the oldest methods of purifying water, and one still used constantly in Third World and often in developing nations or areas that have seen recent natural disasters, is boiling to kill microbes (but this causes loss of taste and may leave in dirt). Other primitive water purifying methods include sand filtering and distilling. But sand filtering does not necessarily kill microbes, and distillation (which heats and traps water as it evaporates) is tedious and only best for removing salt.

Nowadays, however, there are more technologically advanced methods of purifying water.

One of these modern methods is to place water purifiers into a water supply. These mostly involve the use of either tablet forms or liquid forms of iodine. Different formulations are used in different temperature and water condition settings. These iodine water purifiers are often recommended to travelers who are going to a place where the cleanliness of the water supply is suspect.

Chlorine is widely used in pools, needless to say, and some cities and towns use it in limited amounts to cleanse their water supplies, but consumption of chlorine on a regular basis has been linked to cancer and it doesn't taste great, so it is downplayed as a water purifier agent. Chlorine tablets called Halazone tablets used to be supplied by camping stores and given to soldiers to purify water in the wilderness but are no longer recommended unless there's a clear emergency.

People who are afraid of getting poisoned by iodine have been known to use silver tablets to purify water. These silver tablets can be very expensive, but silver has a proven oligodynamic effect, which means it is highly destructive of algae, spores, moulds, fungi, viruses, and bacteria.

Potassium permanganate crystals are the poor man's answer to silver tablets. They're found in any chemical supply store, but they leave a brownish color to the water and they are not as strong as iodine or silver.

The great thing about water purifiers is their portability and delivery into the water.

The most sophisticated water purifying technology involves the use of various commercial water filtering systems. There is a vast array of these filters and their systems, which are specifically designed to meet the wide range of possible water treatment needs of homes, businesses, and communities.

Most of the actual filters are made out of ceramic or charcoal and involve. The water supply is forced through one or more filters, which remove various contaminants or undesired materials but allow the water to continue to pass through to the tap.