Backflush valves are 3-way hydraulically operated diaphragm valves commonly used in filtration applications. The valve has a common outlet connected to the filter inlet and two other outlets, one connected to the water inlet manifold, the other to the drain manifold. The valve can be set in one of two positions: (1) Filtration mode allows flow from the inlet manifold into the filter; and (2) Flushing mode closes the filter connection to the inlet manifold and connects the filter inlet to the drain outlet resulting in reversal flow of filtered water from neighbouring filters through the filter.

The background section contains essential background knowledge on water management and sanitation, covering areas such as health & hygiene, frameworks, economic aspects, environmental aspects, etc.

One of the best ways to clean a water system’s filter is to backwash it, meaning reversing the flow and increasing the velocity at which water passes back through the filter. This, in effect, blasts the clogged particles off of the filter. Although every filter is unique, the principles of backwashing are similar for all of them. The disadvantage with backwashing is that it requires energy-driven pumps and the backwash water and sludge has to be treatment (e.g. in waste stabilisation ponds) before safe discharge or reuse.

Simple, single cell organisms that are found everywhere on earth. They are essential for maintaining life and performing essential “services”, such as composting, aerobic degradation of waste, and digesting food in our intestines. Some types, however, can be pathogenic and cause mild to severe illnesses. Bacteria obtain nutrients from their environment by excreting enzymes that dissolve complex molecules into more simple ones, which can then pass through the cell membrane.

Bank filtration is the infiltration of surface water, mostly from a river system, into a groundwater system induced by water abstraction close to the surface water e.g. a river bank. This water abstraction is commonly done by operating wells. As the water flows through the soil, it is filtered and the quality is improved. In the context of developing or newly-industrialised countries, BF may bring relief by replenishing stressed groundwater resources with surface water, which receives treatment while percolating through the soil and is mixed with the groundwater aquifer.

Bottom / base of the (economic) Pyramid, refers to people around the globe with an income of less than 1,500 USD per annum and capita.

As established by the 2002 World Summit on Sustainable Development (WSSD), basic sanitation means the lowest-cost option for securing sustainable access to safe, hygienic, and convenient facilities and services for excreta and sullage disposal that provide privacy and dignity, while at the same time ensuring a clean and healthful living environment both at home and in the neighbourhood of users.

Basic Services to the Urban Poor

Basin irrigation is the most common form of surface irrigation, particularly in regions with layouts of small fields. If a field is level in all directions, is encompassed by a dyke to prevent runoff, and provides an undirected flow of water onto the field, it is herein called a basin. Basin irrigation is suitable for many field crops. Paddy rice grows best when its roots are submerged in water making basin irrigation the best method for this type of crop.

Batch reactors are reactors with no continuous inflow nor outflow. After the reactor was filled with its content, it is closed for a certain time of reaction. During this time, flow is neither entering nor leaving. After the time of reaction, the now processed liquid or material is removed and replaced by a fresh one and the process cycle can begin again. See also fed batch or accumulating system.

Beneficiary Assessment: conversational interviewing and focus group discussions on changes and impacts.

Compost can also be made in bags or bins with lateral holes to allow aeration. In order to allow proper aeration, the bin is divided into two sections separated with a grid. Organic waste is put into the top section; the final compost it is removed from the bottom section. Because of the natural draught created in the bin by the grid and the holes, frequent turning of the waste is not required in this method.

Bio-char is a fine-grained charcoal produced from pyrolysis: the slow burning of organic matter in a low- or no-oxygen environment. Bio-char is promoted as a soil additive in order to enhance the soil black carbon content and thus the soil water and nutrient retention capacity.

Biodegradable means that a substance is contained of molecules which can be broken down by biological processes (e.g. by bacteria, fungi, and other microorganisms) without causing any harm to them.

Biological transformation of organic material into more basic compounds and elements (e.g., carbon dioxide, water) by bacteria, fungi, and other microorganisms.

A thin, slimy film of bacteria that adheres to surfaces, which are regularly in contact with water. The structure of biofilms is quite complex consisting of colonies of bacteria and other microorganisms such as yeasts, fungi, and protozoa. Biofilms can be a problem for drinking water supply (pipe fouling). But they are also widely used water purification (e.g. biosand filters, slow sand filtration) or in biological wastewater treatment (e.g. rotating biological contactor, trickling filter).

Biogas is the common name for the mixture of gases released from anaerobic digestion. Biogas is comprised of methane (50 to 75%), carbon dioxide (25 to 50%) and varying quantities of nitrogen, hydrogen sulphide, water vapour and other components. Biogas can be collected and burned for fuel (like propane).

In principal, biogas can be used like other fuel gas. When produced in household-level biogas reactors, it is most suitable for cooking. Additionally, electricity generation is a valuable option when the biogas is produced in large anaerobic digesters.

A measure of the amount of oxygen used by microorganisms to degrade organic matter over time (expressed in mg/L and normally measured over five days as BOD5). It is an indirect measure of the amount of biodegradable organic material present in water or wastewater: the more the organic content, the more oxygen is required to degrade it (high BOD). A high BOD can be caused by high levels of organic pollution or high nitrate levels, which trigger high plant growth.

The biological oxygen demand 5 (BOD5) refers to the biological oxygen demand measures over 5 days at 20 ºC.

The biological treatment of waste and wastewaters consist in the use of microbial activity (bacteria, funghi and other microorganisms) for the degradation and decomposing of biodegradable pollution. This is in contrast to chemical treatment, which relies on chemicals to transform or remove contaminants from waste.

Biological wastewater treatment processes are employed to transform dissolved and colloidal pollutants into gases, cell material, and metabolic end products. These processes may occur in the presence or absence of oxygen. In the absence of oxygen (anaerobic process), wastewater materials may be hydrolyzed and the resultant products fermented to produce a variety of alcohols, organic acids, other reduced end products, synthesized cell mass, and gases including carbon dioxide, hydrogen, and methane (biogas). Aerobic processes will generate a variety of oxidized end products, carbon dioxide and metabolized biomass

Biomass refers to plants or animals cultivated using the water and/or nutrients flowing through a sanitation system. It may include fish, insects, vegetables, fruit, forage or other beneficial crops, which can be utilized for food, feed, fibre and fuel production.

Bioremediation is the use of microorganismal metabolism to remove pollutants.

Biosolids, also referred to as treated sludge, is a term used to denote the by-product of wastewater treatment. Biosolids are generally rich in organic matter and nutrients and it can therefore be used as a soil amendment. Depending of the applied wastewater treatment, the resulting biosolids may require further treatment for the removal of pathogens before reuse.

The liquid waste product remaining from sea-salt production; it is highly concentrated in magnesium.

Blackwater is the mixture of urine, faeces and flushwater along with anal cleansing water (if water is used for cleansing) and/or dry cleansing materials. Blackwater contains the pathogens of faeces and the nutrients of urine that are diluted in the flushwater.

Strategic use of development finance and/or philanthropic funds to mobilize private capital to invest in projects or enterprises that promote development outcomes by mitigating the risk of investment (de-risking). Accordingly, the different intents of investors are “blended” in order to reach both positive results for investors and people that get access to products or services at scale.

Blue water footprint is a concept used for water footprint accounting. The blue water footprint is an indicator of the consumption of fresh surface or groundwater.

Boiler feed water is used in various industries for the generation of steam for manufacturing processes. After simple treatment, the water can be reused for various applications.

Border irrigation is a type of surface irrigation where the field is divided into strips separated by border ridges running down the gradient of the field. The area between the ridges is flooded during irrigation. It can be viewed as an extension of basin irrigation to include long rectangular or contoured field shapes, longitudinal but no lateral slope, and free draining or blocked conditions at the lower end. In contrast to basin irrigation bunds are not to contain the water for ponding but to guide it as it flows down the field.

The borehole latrine is an (emergency) excreta disposal system where a borehole (typically 5-10m deep, 40cm in diameter) is combined with a slab and a superstructure. It is an alternative to pit or trench latrines where ground conditions allow it and tools and labour is immediately available locally.

The bottle is first filled up with water and then placed upside down in the ground next to the plant. Because of its density the water is only released slowly into the ground to reach the roots.

Bottled water is widely available in both industrialised and developing countries. Consumers purchase packaged drinking-water for reasons such as taste, convenience or fashion, but safety and potential health benefits are also important considerations.
Bottled water is most commonly sold in glass or disposable plastic bottles. Bottled water also comes in various sizes, from single servings to large carboys holding up to 80 litres.

Boundary kits isolate individual properties from the main pressure sewer network and can be installed prior to the individual pumping units. This allows for individual properties to connect at a rate that suits the development whilst also allowing fast and simple isolation if required.

Brackish water contains more salt than fresh water and less than salt water. It is commonly found in estuaries, which are the lower courses of rivers where they meet the sea, and aquifers, which are stores of water underground.

Brownwater is the mixture of faeces and flushwater, and does not contain urine. It is generated by urine-diverting flush toilets and, therefore, the volume depends on the volume of the flushwater used. The pathogen and nutrient load of faeces is not reduced, only diluted by the flushwater. Brownwater may also include Anal Cleansing Water (if water is used for cleansing) and/or Dry Cleansing Materials.

Embankment constructed from soil or wadi bed sediments.

A company’s business model is the mechanism through which it generates its profit.

The Business Model Canvas is an entrepreneurial tool for describing, designing, challenging, analysing, inventing and pivoting business models.

The business plan is a document presenting the company's strategy and expected financial performance. It serves as roadmap to the success of your business and is vital for any newly starting enterprise.

Replication means duplication of a proven business idea in a different geographical region or context. Successful business ideas can inspire individuals or groups to replicate a specific business idea. In the context of safe water provision, replication of existing ideas is highly encouraged in terms of learning from others.

Business scaling describes the growth of a business in terms of reaching more costumers and increasing product/service sales accordingly.