Ultraviolet radiation spans wavelengths from about 10 nm to 400 nm and is an important component of sunlight although the ozone layer prevents much of it from reaching the earth's surface. It is seperated in UV-A, UV-B and UV-C light. UV-C and UV-B light have a damaging effect on DNA and can therefore act as a desinfectant (killing microbes) or cause skin cancer and genetic mutation.

A kind of low-pressure membrane filtration process in which hydrostatic pressure forces a liquid against a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained, while water and low molecular weight solutes pass through the membrane (typically with a pore size of l 0.1–to 0.01 micrometres).

Saturated permeable soil (sand or gravel) not capped by an impermeable layer.

As defined by the Joint WHO & UNICEF Monitoring Programme (JMP), an unimproved drinking-water source is one that by the nature of its construction does not adequately protect the source from outside contamination, in particular with faecal matter. Unimproved drinking-water sources include: Unprotected (dug) well; unprotected spring, cart with small tank or drum; tanker truck-provided water, surface water (river, dam, lake, pond, stream, canal, irrigation channel); bottled water (because of potential limits on the quantity of water available to a household through this source, not the quality).

United Nations

United Nations Children’s Fund

United Nations Commission on Sustainable Development

United Nations High Commission for Refugees, that is, the UN Refugee Agency

An unplanted drying bed is a simple, permeable bed that, when loaded with sludge, collects percolated leachate and allows the sludge to dry by evaporation. Approximately 50% to 80% of the sludge volume drains off as liquid or evaporates. The sludge, however, is not effectively stabilized or sanitized. Unplanted drying beds need to be desludged regularly. The percolate or leachate needs to be collected and treated before reuse or disposal. See also planted drying beds.

The unsaturated zone is the portion of the subsurface above the groundwater table. The soil and rock in this zone contains air as well as water in its pores. In some places the unsaturated zone is absent, as is common where there are lakes and marshes, and in some places it is hundreds of meters thick, as is common in arid regions. Hydrologically, the unsaturated zone is often the main factor controlling water movement from the land surface to the aquifer. Flow rates and chemical reactions in the unsaturated zone control whether, where, and how fast contaminants enter groundwater supplies.

The upflow anaerobic sludge blanket reactor (UASB) is a single tank process used for the biological treatment of wastewater. Wastewater enters the reactor from the bottom, and flows upward. A suspended sludge blanket filters and treats the wastewater as the wastewater flows through it. Biogas, which is produced during the process can be collected and reused. Effluent requires a further treatment step to remove pathogens. Sludge can be composted and/or dried before safe disposal or reuse in agriculture as soil amendment.

The upstream / downstream conflict over water consists of diametrically opposed demand patterns for water resources, in space and in time. Furthermore, downstream communities often suffer from upstream induced pollution.

Urban Infrastructure Development Scheme for Small and Medium Towns (UIDSSMT) of the Government of India is sponsored by the Government of Karnataka. UIDSSMT aims at improvement in urban infrastructure in towns and cities in a planned manner. UIDSSMT will subsume the existing schemes of Integrated Development of Small and Medium Towns (IDSMT) and accellerated Urban Water Supply Scheme (AUWSP).

Urban Local Body

The organic molecule (NH2)2CO that is excreted in urine and that contains the nutrient nitrogen. Over time, urea breaks down into carbon dioxide and ammonium, which is readily used by organisms in soil.

A urinal is used only for collecting urine. Urinals are generally for men, although models for women have also been developed. Most urinals use water for flushing, but waterless urinals are becoming increasingly popular.

Urine is the liquid produced by the body to rid itself of urea and other waste products. In this context, the urine product refers to pure urine that is not mixed with faeces or water. Depending on diet, human urine collected from one person during one year (approx. 300 to 550 L) contains 2 to 4 kg of nitrogen. With the exception of some rare cases, urine is sterile when it leaves the body.

Urine diversion devices collect urine separately from faeces and from water (or with minimal flush water). A urine diversion toilet has two outlets with two collection systems: one for urine and one for faeces in order to keep these two excreta or wastewater fractions separate.

Urine diversion components allow toilet users to separate urine from faeces. There are urine diversion components for all kind of toilet systems, cultures and climates.

A Urine Diverting Dry Toilet (UDDT) is a toilet that operates without water and has a divider so that the user, with little effort can divert the urine away from the faeces.

Urine storage is the simplest and cheapest way to hygienise separately collected urine in order to reuse it safely in agriculture. Urine is generally sterile but contains most of the plant nutrients excreted by humans. To hygienise urine, it is stored for one up to six or more month, depending on estimated risk of cross-contamination with faeces. The sanitising effect comes from a combination of the rise of pH (due to the transformation of urea to ammonium by the naturally present enzyme urease), the raise of temperature and time.

When urine cannot be used immediately or transported using a conveyance technology (e.g. jerrycans), it can be stored onsite in containers or tanks. The storage tank must then be moved or emptied into another container for transport.

The urine-diverting flush toilet is similar in appearance to a cistern flush toilet except for the diversion in the bowl. The toilet bowl has two sections so that the urine can be separated from the faeces. Both sitting and squatting models exist. See also urine diversion components.

Refers to the sanitation methods by which products are ultimately returned to the environment, either as useful resources or reduced-risk materials. Furthermore, sanitation products can also be cycled back into a system (e.g., by using treated greywater for flushing).

User Interface describes the ways of collecting, storing, and sometimes treating the products generated at the User Interface. The treatment provided by these technologies is often a function of storage and is usually passive (e.g., requiring no energy input). Thus, products that are ‘treated’ by these technologies often require subsequent treatment before Use and/or Disposal.

The longest ultraviolet radition, UV-A, lies within 315 and 400 nm. Most of it passes through the atmosphere and reaches the earth surface.

Ultraviolet radiation within 280 and 315 nm. UV-B can be directly absorbed by DNA and is therefore carcinogenic and can kill microorganisms. Most of it in natural sunlight is filtred out by the ozone layer and only some few percent of the solar spectre contain UV-B.

Ultraviolet radation within 100 and 280 nm. Almost all of UV-C light from the natural solar light is filtred out in the atmosphere.