A reverse osmosis water purification unit (ROWPU) is a portable, self-contained water treatment

Water purification

Water purification is the process of removing undesirable chemicals, materials, and biological contaminants from contaminated water. The goal is to produce water fit for a specific purpose...

 plant. Designed for military use, it can provide potable

Drinking water

Drinking water or potable water is water pure enough to be consumed or used with low risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually...

 water from nearly any water source. There are many models in use by the United States armed forces

United States armed forces

The United States Armed Forces are the military forces of the United States. They consist of the Army, Navy, Marine Corps, Air Force, and Coast Guard.The United States has a strong tradition of civilian control of the military...

 and the Canadian Forces

Canadian Forces

The Canadian Forces , officially the Canadian Armed Forces , are the unified armed forces of Canada, as constituted by the National Defence Act, which states: "The Canadian Forces are the armed forces of Her Majesty raised by Canada and consist of one Service called the Canadian Armed Forces."...

. Some models are containerized

Containerization

Containerization is a system of freight transport based on a range of steel intermodal containers...

, some are trailers, and some are vehicles unto themselves.

Each branch of the United States armed forces has their own series of ROWPU models, but they are all similar. The water is pumped from its raw source into the ROWPU module, where it is treated with a polymer

Polymer

A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

 to initiate coagulation

Coagulation

Coagulation is a complex process by which blood forms clots. It is an important part of hemostasis, the cessation of blood loss from a damaged vessel, wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel...

. Next, it is run through a multi-media filter where it undergoes ion exchange

Ion exchange

Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic 'ion...

. It is then pumped through a cartridge filter which is usually spiral-wound cotton. This process clarifies the water of any particles larger than 5 micrometre (0.000196850393700787 in) and eliminates almost all turbidity

Turbidity

Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality....

.

The clarified water is then fed through a high-pressure piston pump into a series of vessels where it is subject to reverse osmosis

Reverse osmosis

Reverse osmosis is a membrane technical filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and...

. The product water is free of 90.00–99.98% of the raw water's total dissolved solids

Total dissolved solids

Total Dissolved Solids is a measure of the combined content of all inorganic and organic substances contained in a liquid in: molecular, ionized or micro-granular suspended form. Generally the operational definition is that the solids must be small enough to survive filtration through a sieve...

 and by military standards, should have no more than 1000–1500 parts per million

Parts-per notation

In science and engineering, the parts-per notation is a set of pseudo units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement...

 by measure of electrical conductivity. It is then disinfected with chlorine

Chlorine

Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

 and stored for later use.

Within the United States Marine Corps

United States Marine Corps

The United States Marine Corps is a branch of the United States Armed Forces responsible for providing power projection from the sea, using the mobility of the United States Navy to deliver combined-arms task forces rapidly. It is one of seven uniformed services of the United States...

, the ROWPU has been replaced by both the Lightweight and Tactical Water Purification Systems. They are HMMWV

High Mobility Multipurpose Wheeled Vehicle

The High Mobility Multipurpose Wheeled Vehicle , better known as the Humvee, is a military 4WD motor vehicle created by AM General. It has largely supplanted the roles formerly served by smaller Jeeps such as the M151 MUTT, the M561 "Gama Goat", their M718A1 and M792 ambulance versions, the CUCV,...

- and medium tactical vehicle replacement

Medium Tactical Vehicle Replacement

Medium Tactical Vehicle Replacement or 7-Ton, is a six-wheel drive all-terrain vehicle used by the United States Marine Corps and United States Navy....

-mounted, respectively, and can filter 125 and 1500 imp gal (568.3 and 6,819.1 l) per hour.