Ways That Water Is Filtered

The slow sand filter was the first filter developed for large-scale water filtration.

Approximately 70 percent of the Earth is covered in water. But less than 2 percent of that water is categorized as "fresh water," having a chemical balance or salt content safe for humans to drink directly. Despite its name, fresh water usually contains additional impurities like mud and other toxins that make it less than palatable if consumed without prior treatment.

Purification versus Filtration

The terms "water purification" and "water filtration" are sometimes used interchangeably for common usage, but they actually have different meanings. Water purifiers kill bacteria and viruses while filters can only remove bacteria. However, filtration removes solid material from water, whereas purification alone does not.

Outdoor Emergencies

Many water filters are specifically designed for outdoor use, such as during camping. These outdoor filters can be purchased online and at specialty or retail stores. In a pinch, however, a makeshift water filter can be created by using a plastic container, sand, gravel and either pebbles or material made from cotton.

First, poke small holes into the bottom of the container. Add approximately 1 inch of pebbles or cotton material to the container, followed by 2 inches of gravel. Fill the container with sand, as much as allowable, up to 6 inches. Pour the water you want to filter into the container. Place a second container below the device to catch the filtered water.

Distribution Systems

In 1974, Congress passed the Safe Drinking Water Act. The bill established maximum levels for contaminants in water treated by the nation's public and commercial distribution systems. Filtering water through distribution systems generally involves a combination of chemical and physical processes. Some of the filtration methods used by these systems include diatomite, rapid sand, slow sand and pressure.

Diatomite Filters

Diatomite or, more formally, diatomaceous earth filtration, uses a form of crushed sedimentary rock (diatomaceous earth) to strain out impurities via vacuum, gravity or pressurized force. Water filtered through these systems requires chemical pre-treatment to maximize the filtration process. Many of these filters are used in swimming pools and in the food and beverage industry.

Rapid Sand Filters

Rapid sand filters are gravity-driven devices, commonly utilized for surface water treatment. Chemicals must be applied to the water prior to filtration. Contaminants are absorbed by sand or a combination of sand with garnet and/or anthracite coal.

Slow Sand Filters

Water filtered through slow sand filters do not require chemical pre-treatment. This filtration method is primarily used in groundwater system applications. Slow sand filters capitalize on gravitational forces, utilizing sand to strain, absorb and biologically react with water impurities.

Pressure Filters

Pressure filters use pressurized force in conjunction with rapid sand filters. These filters absorb manganese and iron from water in groundwater systems. Water sent through pressure filters does not need chemical pre-treatment.

References

• Encyclopedia.com: Encyclopedia of Public Health -- Water Treatment
• Encyclopedia.com: UXL Encyclopedia of Science - Filtration
• Berkey Filters: A Filter is different than a Purifier
• Wilderness Survival Skills: How to Make a Water Filter
• Mountain Empire Community College: Types of Filters
• West Virginia University - The National Environmental Services Center: Filtration