Rainwater harvesting refers to the capturing and storing of rainwater and the taking of measures to keep it clean. Rainwater can be harvested through a variety of ways: capturing the rain on rooftops or its run-off (e.g. seasonal flood water) in local catchment systems (e.g. rock catchment, subsurface or surface dams). Rain collected from rooftops or small-scale rock catchments is generally used for domestic use, while large-scale rock catchment, ground catchment and dam catchment systems are used for livestock, nurseries, small-scale irrigation and only sometimes for domestic use.

Raipur Municipal Corporation

Guidelines for slum-free city planning of the Ministry of Housing & Urban Poverty Alleviation, India.

Rapid sand filters can be constructed as gravity filters. They are used for water purification purposes and essentially consist of an open-topped box (usually made of concrete), drained at the bottom, and partly filled with a filtering medium. Fresh water is admitted to the space above the medium and flows downward under the action of gravity. Purification takes place during this downward passage and the treated water is discharged through the under-drains.

Rapid sand filtration is a physical drinking water purification method. As freshwater flows through a sand- and gravel bed, the majority of suspended particles are removed. Rapid sand filters provide rapid and efficient removal of relatively large suspended particles but they cannot provide safe drinking water unless pre-treatment (i.e. coagulation-flocculation) and post-treated (e.g. chlorine disinfection) is applied.

ROS are chemically-reactive molecules containing oxygen. Examples include oxygen ions and peroxides. Reactive oxygen species are highly reactive due to the presence of unpaired valence shell electrons. ROS form as a natural byproduct of the normal metabolism of oxygen and have important roles in cell signaling. However, during times of environmental stress (e.g. UV or heat exposure) ROS levels can increase dramatically. This can result in significant damage to cell structures. This cumulates into a situation known as oxidative stress.

A container or apparatus in which substances are made to react chemically.

Recharge or injection wells are subsurface groundwater recharge techniques used to directly discharge water into deep water-bearing zones. Recharge wells can be cased with the material covering the aquifer. If this material is unconsolidated, a screen can be placed in the well in the zone of injection. Recharge wells are suitable only in areas where a thick impervious layer exists between the surface of the soil and the aquifer that is to be replenished. They are also advantageous in areas where land is scarce (as [2022-surface groundwater recharge] requires large areas for infiltration). A relatively high rate of recharge can be attained with this method.

A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion.

Reclaimed water, sometimes called recycled water, is former wastewater (e.g. treated blackwater and greywater; stormwater) that has been treated to remove solids and certain organic or microbiological pollution in order to be used in agriculture, or to recharge groundwater aquifers. This is done for sustainability and water conservation, rather than discharging the treated wastewater to surface waters such as rivers and oceans.

The recovery phase describes the third period following an event. Different communities affected by the same event may experience different speeds of recovery. It typically starts 2-6 months after the event and lasts up to 1 year (DAVIS & LAMBERT 2002). Harvey (2007) estimates that the stabilisation and recovery phase together last for several months or several years after the event, depending on the type and severity of the emergency. The exact duration depends on the event and the context of the emergency. Duration is not time-bound but rather depends on the achievement of set targets (indicators).

A refrigerator is an appliance or compartment that is artificially kept cool and used to store food and drinks for example. Modern refrigerators generally make use of the cooling effect produced when a volatile liquid is forced to evaporate in a sealed system in which it can be condensed back to liquid outside the refrigerator.

A person who has been forced to leave his or her country of permament residence in order to escape war, persecution, or natural disaster.

A person who has been forced to leave his or her country of permament residence in order to escape war, persecution, or natural disaster.

Rehabilitate, Opearate and Transfer (ROT) is a contractual arrangement whereby an existing facility is turned over to the private sector to refurbish, operate and maintain for a franchise period, at the expiry of which the legal title to the facility is returned to the government.

Water allocation (see also water allocation) is associated with a certain probability that it will be supplied because river flows vary with time. This reliability of supply has to be high for sanitation.

Resource Recovery and Reuse promotes a paradigm shift in solid and liquid waste management from treatment for disposal to treatment for reuse. RRR offers significant value beyond “ecological benefits” by offering viable options for cost recovery in the recovering of nutrients, water and energy from domestic and agro-industrial waste streams.

Restrictions and prohibitions are a part of command & control tools which are regulatory instruments that are direct and mandatory. Restrictions, rationing or full prohibitions are legal prescriptions that have a direct impact on the range of options open to specified social actors, as they constrain certain ways of acting or exclude some forms of conduct. Public authorities or independent regulatory agencies establish restrictions and bans which, in the case of restrictions in water use, water and land users as well as water service providers are obliged to follow.

A person or business that sells a product to a customer either as single or multiple offers.

Retention basins are among the most frequently implemented storm water management systems. They are used to collect surface runoff and to improve water quality by natural processes such as sedimentation, decomposition, solar disinfection and soil filtration. In comparison to dry ponds (which hold runoff for a limited period of time and then release the stored water at once), retention basins constantly keep standing water allow for the development of an ecosystem. This allows settled particles to be treated biologically (GDSDS 2005). Water from retention ponds can be reused for groundwater recharge, irrigation or any other purpose, after further treatment if required. As a natural system, retention basins do not require energy or high-tech appliances. Primary implementation costs of retention basins are high and constant maintenance is inevitable, as otherwise pollutant export and erosion can occur (UNHSC 2010).

By analysing past rainfall records, it is possible to make an estimate of the probability of any particular rate occurring. The more severe the rainstorm (i.e. the higher the rate of rainfall), the lower the probability of it occurring. This probability is usually expressed as a “return period”. A rainstorm with a probability of 1 in 20 of occurring in any particular year is said to have a return period of 20 years for instance, and is called a 20-year storm. This does not mean that it occurs exactly every 20 years but five times a century on average.

Use of recycled water.

In order to optimise water and nutrient exploitation and close the cycle at a local level, pre-treated wastewater, urine or hygienised faeces may be reused in agriculture.

The organic fraction of waste and wastewater can be transformed into renewable fuels in the form of biogas or burnable biomass. This can be used to produce energy.

In order to optimise the nutrient and water cycle at a local level and to achieve food security, the nutrients contained in urine and faeces can be reused as fertiliser to produce agricultural products.

Osmosis is a natural phenomenon in which water passes through a semipermeable barrier from the side with lower solute concentration to the higher solute concentration side. Water flow continues until chemical potential equilibrium of the solvent is established. At equilibrium, the pressure difference between the two sides of the membrane is equal to the osmotic pressure of the solution. To reverse the flow of water (solvent), a pressure difference greater than the osmotic pressure difference is applied; as a result, separation of water from the solution occurs as pure water flows from the high concentration side to the low concentration side. This phenomenon is termed reverse osmosis (it has also been referred to as hyperfiltration).
A reverse osmosis (R-O) membrane acts as the semipermeable barrier to flow in the R-O process, allowing selective passage of a particular species (solvent, usually water) while partially or completely retaining other species (solutes).

Rhizofiltration is a form of bioremediation that involves filtering water through a mass of roots to remove toxic substances or excess nutrients.

The right to water entitles every person to access a sufficient amount of clean and affordable water for personal and domestic use. The right to sanitation is access to, and use of, excreta and wastewater facilities and services that ensure privacy and dignity. Enforcing both the right to water and sanitation is an important condition in protecting the quality of drinking water. Both rights are contained in Art. 11 and 12 of the International Covenant on Economic, Social and Cultural Rights as well as numerous other important international legal documents. States parties have an obligation to respect, protect and fulfil the right to water and sanitation. The right to water and sanitation provides clear sest of principles and goals to guide policy development and implementation through translation into national legislation.

Rill erosion occurs as runoff begins to form small concentrated channels. As rill erosion begins, erosion rates increase dramatically due to the resulting concentrated higher velocity flows. Rill can be repaired by tilling or normal cultivation operation and should be repaired as soon as possible in order to prevent gullies from forming.

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including stream, creek, brook, rivulet, tributary and rill.

River regime can described as one of two characteristics of a reach of an alluvial river: (1) The variability in its discharge throughout the course of a year in response to precipitation, temperature, evapotranspiration, and drainage basin characteristics and (2) a series of characteristic power-law relationships between discharge and width, depth, and slope.

Rooftop rainwater harvesting is the most common type of rainwater harvesting (RWH) for domestic use. It is a simple low-cost technique that requires a minimum of specific expertise and that offers many benefits. Rainwater is collected on the roof and transported to a storage reservoir via gutters, where it supplies water at the point of use. Rainwater harvesting can supplement other water sources when they become scarce or are of low quality like brackish groundwater or polluted surface water in the rainy season. However, rainwater quality may be affected by air pollution, animal or bird droppings, insects, dirt and organic matter. Therefore regular maintenance (cleaning, repairs, etc.) and treatment before water use is very important (e.g. filtration or/and disinfection).

Rotating biological contactors (RBC), also called rotating biological filters, are fixed bed reactors consisting of stacks of rotating disks mounted on a horizontal shaft that are partially submerged in a reactor and rotated as wastewater flows through. They are used in conventional wastewater treatment plants as secondary treatment after primary sedimentation of domestic grey- or blackwater or any other biodegradable effluent. The microbial community is alternately exposed to the atmosphere and the wastewater allowing both, aeration and assimilation of dissolved organic pollutants and nutrients for their degradation.

Roughing filters are used to separate solid matter from water. Some solid particles suspended in water are so small and light that they do not settle in a normal sedimentation tank. The same sedimentation tank can be improved by filling it with rough filter material such as gravel. Roughing filters usually consist of sedimentation tanks filled with differently sized filter material decreasing successively in size in the direction of flow. The bulk of solid particles is separated by the coarse filter medium located next to the filter inlet. The subsequent medium and fine filter media further reduce the concentration of suspended solids. Roughing filters are operated with small hydraulic loads - filtration velocity is usually about 0.3-1.5 m/h.

The portion of precipitation that does not infiltrate the ground and runs overland.

The assignment of the runoff coefficient (C) is somewhat subjective. At the time the runoff producing rainfall occurs, the coefficient varies with topography, land use, vegetal cover, soil type and moisture content of the soil. In selecting the runoff coefficient, consider the future characteristics of the watershed. If land use varies within a watershed, you must consider watershed segments individually, and you can calculate a weighted runoff coefficient value.

Rural Water Supply and Sanitation Unit