Water reclamation is the process of turning wastewater from cities, farms, or industries into water that can be used again for different purposes. It is also called wastewater reuse, water reuse, or water recycling. Water can be reused in cities, for farming, or to help the environment. Other uses include industrial processes and, in some cases, for drinking water. Reused water can be used to water plants, refill lakes and underground water sources, or help clean the environment. This process of adding water back to underground sources is called groundwater recharge. Reused water can also be used in homes for tasks like flushing toilets, in businesses, and in factories. Wastewater can be treated to meet drinking water standards. When treated wastewater is added directly to the water supply system, it is called direct potable reuse. Drinking reclaimed water is not common. Using treated wastewater for farming is a long-standing practice, especially in dry areas. Reusing wastewater helps provide more water for people and reduces the need to use limited natural water sources. It also helps protect groundwater and other water supplies.

Several methods are used to treat wastewater for reuse. These methods can work together to make sure the water is clean and safe, meaning it has no harmful germs. Common methods include ozonation, ultrafiltration, aerobic treatment (using membrane bioreactors), forward osmosis, reverse osmosis, advanced oxidation, and activated carbon. Some activities, like watering plants, do not need very clean water. In these cases, wastewater can be reused with little or no treatment.

In many parts of the world, reclaimed water costs more than fresh water when fresh water is available in large amounts. The cost of water reclamation can be compared to other methods that also save fresh water, such as using greywater (wastewater from sinks and showers), collecting rainwater, capturing stormwater, or desalinating seawater.

Water recycling and reuse are becoming more important in dry areas, cities, and places with polluted water. Cities in the Middle East and North Africa, such as the United Arab Emirates, Qatar, Kuwait, and Israel, use municipal wastewater reuse more than other regions.

Definition

The term "water reuse" is often used the same way as terms like wastewater reuse, water reclamation, and water recycling. According to the USEPA, water reuse means recycling treated wastewater for useful purposes, such as watering crops, landscapes, and lawns, using water in factories, flushing toilets, and adding water back into underground sources (EPA, 2004). A similar explanation states: "Water reuse involves using treated wastewater that has been cleaned and made safe for specific uses. This practice has been used for a long time in many areas with little rain. It helps reduce water shortages by adding to the limited supply of fresh water."

The water used in treatment and reuse processes can come from different sources. Most often, it is wastewater from homes, cities, industries, or farms. However, it may also come from rainwater that flows over streets and roads.

Overview

Reclaimed water is water that is used more than once before it returns to the natural water cycle. Improvements in wastewater treatment technology allow communities to reuse water for many purposes. The treatment process varies based on the water's source, intended use, and how it is delivered.

The World Health Organization lists these main reasons for reusing wastewater:
1. Growing water shortages and stress,
2. Increasing populations and related challenges with food supply,
3. Environmental harm caused by improper wastewater disposal, and
4. Greater recognition of the value of wastewater, excreta, and greywater as resources.

In some areas, advanced wastewater treatment to remove tiny organic pollutants improves water quality.

Water recycling and reuse are becoming more important, not only in dry regions but also in cities and polluted areas. Groundwater sources, used by over half the world’s population, are being overused. As the global population grows and becomes more concentrated near coasts, where freshwater is limited, reuse will increase. Using treated wastewater can save large amounts of freshwater, reduce pollution, and lower the environmental impact of water use. Reuse can also serve as an alternative water supply.

To achieve more sustainable sanitation and wastewater management, efforts must focus on resource management, such as reusing wastewater or excreta for productive purposes. This supports human health and overall sustainability.

Using reclaimed water as an alternative water source offers economic, social, and environmental benefits, which drive reuse programs. These benefits include:
• For cities and homes: More water availability (using reclaimed water for non-drinking purposes like industry, cleaning, irrigation, and toilet flushing, while saving drinking water for consumption).
• For the environment: Less pollution from nutrients in waterways (such as rivers and canals); reduced overuse of surface and groundwater; better protection of ecosystems like streams and wetlands; and lower energy use for water production, treatment, and delivery (1.2 to 2.1 kWh/m³) compared to using deep groundwater, importing water, or desalination.
• Lower costs for using high-quality reclaimed water in manufacturing.
• In agriculture: Treated wastewater used for irrigation can increase crop yields, reduce environmental harm, and support economic and social benefits. It may also reduce fertilizer use by providing nutrients from treated wastewater to soil.

Using reclaimed water instead of freshwater can save water. When used water returns to natural sources, it can help ecosystems by improving water flow, supporting plant life, and recharging groundwater as part of the natural water cycle.

Globally, about 40.7 billion cubic meters of treated wastewater are reused each year, which is about 11% of total domestic and industrial wastewater. Municipal wastewater reuse is especially common in the Middle East and North Africa, including countries like the UAE, Qatar, Kuwait, and Israel.

For the United Nations’ Sustainable Development Goal 6, Target 6.3 states: "Halve the proportion of untreated wastewater and significantly increase recycling and safe reuse globally by 2030."

Types and applications

Treated wastewater can be reused in many ways. It is used in industry, such as in cooling towers, to help recharge underground water sources, in farming, and to help restore natural areas like wetlands. The most common uses of reclaimed water around the world include:

In some cases, reclaimed water is also used to supplement drinking water supplies. Most reclaimed water uses are for non-drinking purposes, such as washing cars, flushing toilets, cooling power plants, mixing concrete, creating artificial lakes, watering golf courses and public parks, and for hydraulic fracturing. When possible, systems use two separate pipe systems to keep recycled water apart from drinking water.

There are two main categories of reclaimed water use:

• Unrestricted: Reclaimed water used for non-drinking purposes in public areas where people can access it freely.
• Restricted: Reclaimed water used for non-drinking purposes in public areas where access is limited by barriers like fences, signs, or rules that control when or how people can use it.

Recycled wastewater used for farming can help fertilize plants if it contains nutrients like nitrogen, phosphorus, and potassium. Benefits of using recycled water for irrigation include lower costs compared to other water sources and a steady supply of water regardless of the season or weather. When reclaimed water is used in agriculture, the nutrients in the treated wastewater can act as fertilizer. This makes the reuse of waste from sewage more appealing.

Recycled water can be used in different ways for different crops. For example, it can be used to water crops that are eaten raw or for crops that are processed (like cooked or industrially prepared food). It can also be used for crops not meant for human consumption, such as pastures, forage, fiber, ornamental plants, seeds, forest crops, or turf.

In developing countries, farmers often use untreated wastewater for irrigation, which can be unsafe. Cities offer good markets for fresh produce, so farmers are drawn to them. However, because water is becoming scarcer due to competition from industry and other users, farmers may have no choice but to use polluted water to grow crops.

Using untreated wastewater in farming can cause serious health risks. Municipal wastewater may contain harmful chemicals and disease-causing organisms. In low-income countries, untreated wastewater often has high levels of germs from human waste. In some developing nations, the rapid growth of industry has increased risks from harmful chemicals. The World Health Organization created guidelines in 2006 to help safely use wastewater. These guidelines suggest steps like stopping irrigation a few days before harvesting to let germs die in the sun, applying water carefully to avoid contaminating edible parts of plants, cleaning vegetables with disinfectants, or drying waste before using it as fertilizer.

Using reclaimed water can have both good and bad effects on soil and plants. The impact depends on the type of wastewater and the characteristics of the soil or plants.

Using reclaimed water to create or improve water bodies like wetlands, aquatic habitats, or streams is called "environmental reuse." For example, wetlands built with wastewater can treat water while also supporting plant and animal life.

Treated wastewater can be reused in industry, such as in cooling towers.

Planned potable reuse is when water is intentionally recycled for drinking. There are two main ways to reuse water for drinking: "Indirect Potable Reuse" (IPR) and "Direct Potable Reuse" (DPR). Both methods require formal public processes and discussions.

Some water agencies use highly treated wastewater as a reliable source of drinking water, especially during droughts. Advanced purification methods ensure the water meets all safety standards. System reliability and regular testing are essential to maintaining safety.

A community’s water needs, available water sources, public health rules, costs, and existing water infrastructure determine whether reclaimed water can be used for drinking. Some areas use reclaimed water to refill underground water sources, while others add it to surface water reservoirs. In these cases, reclaimed water is mixed with other water supplies or stored for a time before being treated again. In some places, reclaimed water is sent directly into pipelines that lead to treatment plants or distribution systems.

Modern technologies like reverse osmosis and ultraviolet disinfection are often used when reclaimed water is mixed with drinking water.

Some people feel uncomfortable about using reclaimed water for drinking. In one survey, 13% of people said they would not even sip it. However, the main health risk of using reclaimed water for drinking is the possibility of harmful chemicals, like pharmaceuticals or household products, remaining in the water. This risk could be reduced if human waste was kept separate from sewage through systems like dry toilets or by treating blackwater (waste from toilets) separately from greywater (waste from sinks and showers).

Indirect Potable Reuse (IPR) means water is delivered to consumers indirectly. After being purified, the water is mixed with other water supplies or stored in natural or man-made areas, such as underground aquifers or surface reservoirs, before being sent to treatment plants or distribution systems.

Some cities are using or studying IPR to reuse reclaimed water. For example, reclaimed water may be pumped into underground water sources, allowed to seep into the ground, and then pumped out, treated again, and used as drinking water. This process is sometimes called groundwater recharging. It involves additional purification steps as water passes through layers of soil and is broken down by natural processes.

IPR or unplanned use of reclaimed water for drinking is common in many countries. In some places, wastewater is released into groundwater to prevent saltwater from seeping into freshwater sources near the coast. IPR often includes natural barriers, but in some areas, more direct methods are needed.

IPR happens when treated municipal wastewater is added to drinking water supplies.

Design considerations

Non-potable reclaimed water is often delivered using two separate pipe systems. These systems keep reclaimed water pipes completely apart from pipes that carry drinkable water.

Several methods are used to treat wastewater so it can be reused. Combining these methods helps meet strict safety standards and ensures the treated water is free from harmful germs. Common methods include using ozone gas, ultrafiltration, aerobic treatment (membrane bioreactor), forward osmosis, reverse osmosis, advanced oxidation, or activated carbon. Reclaimed water providers use multiple treatment steps and ongoing checks to confirm the water is safe and properly treated for its intended use.

Some activities do not need high-quality water. In these cases, wastewater can be reused with little or no treatment. For example, in homes, greywater from baths and showers can be used to flush toilets without much treatment.

For municipal wastewater, the water must go through several treatment steps before it can be reused. These steps may include screening, primary settling, biological treatment, tertiary treatment (such as reverse osmosis), and disinfection.

Wastewater is usually treated only to a secondary level when it is used for irrigation.

A pump station sends reclaimed water to users across a city. These users may include golf courses, farms, cooling towers, or landfills.

Instead of treating municipal wastewater for reuse, other methods can save freshwater:
– Greywater reuse systems: At homes, treated or untreated greywater may be used for flushing toilets or watering gardens.
– Rainwater harvesting and stormwater recovery: Systems that collect rainwater and reduce runoff are called water-sensitive urban design (WSUD) in Australia, low-impact development (LID) in the United States, and sustainable urban drainage systems (SUDS) in the United Kingdom.
– Seawater desalination: This energy-heavy process removes salt and minerals from seawater to make drinkable water. It is usually done through membrane filtration (reverse osmosis) or steam distillation.

In many regions, reclaimed water is more expensive than drinkable water because fresh water is plentiful. However, reclaimed water is often sold at a lower price to encourage its use. As fresh water becomes scarcer due to distribution costs, population growth, or climate change, the cost comparison may change. Evaluating reclaimed water should consider the entire water supply system, as it can add flexibility to the system.

Reclaimed water systems typically require two separate pipe systems, often with extra storage tanks, which increases the system’s cost.

Barriers to water reclamation may include:
– Large-scale water reuse projects face challenges related to rules, money, public opinion, and organizational systems.
– Water reuse projects may not be economically viable because of the costs of checking water quality and identifying contaminants. Identifying contaminants can be difficult, as it involves separating inorganic and organic pollutants, microorganisms, colloids, and others. It is hard to fully recover the costs of water reuse projects. There is also a lack of financial systems for water pricing that match the support given to traditional treatment plants.
– Psychological barriers, such as the "yuck factor," can also stop reuse projects, especially for direct potable reuse. These barriers are linked to feelings of disgust, particularly related to avoiding germs.

Health aspects

Reclaimed water is safe when used correctly. Water that is planned for use in refilling underground water sources or adding to surface water receives proper treatment before mixing with natural water and undergoing natural cleaning processes. Some of this water may later become part of drinking water supplies.

A study from 2009 compared the quality of reclaimed water, surface water, and groundwater. The results showed that these water types are more similar than different in terms of the substances they contain. Researchers tested for 244 common substances found in water. Most substances were found in very small amounts, measured in parts-per-billion or parts-per-trillion. DEET (an insect repellent) and caffeine were found in all water types and most samples. Triclosan (a chemical in antibacterial soap and toothpaste) was found in all water types, but in slightly higher amounts in reclaimed water than in surface or groundwater. Very few hormones and steroids were found, and when present, they were at extremely low levels. Haloacetic acids (a byproduct of water disinfection) were found in all water types, including groundwater. The biggest difference between reclaimed water and other water types is that reclaimed water has been treated with disinfectants, which can create disinfection byproducts.

A 2005 study found no cases of illness or disease caused by microbes or chemicals in reclaimed water. The risk of using reclaimed water for irrigation is not significantly different from using clean drinking water for irrigation.

A 2012 study by the National Research Council in the United States found that the risk of exposure to certain microbes and chemicals from drinking reclaimed water does not appear to be higher than the risk in some current drinking water systems. It may be much lower. The report suggested changes to federal rules to improve public health protection for both planned and unplanned (or de facto) reuse and to increase public trust in water reuse.

Environmental aspects

Using reclaimed water for tasks that do not require drinking water helps save drinking water for people to use, because less drinking water is needed for these tasks.

Reclaimed water may have more nutrients, such as nitrogen, phosphorus, and oxygen, which can help plants grow when used for watering gardens or crops.

Freshwater makes up less than 3% of the world’s water, and only about 1% of that is easily accessible. Even though freshwater is limited, only 3% of it is used for people’s needs. Most of the remaining freshwater is used for agriculture, which uses about two-thirds of all freshwater globally.

Reclaimed water can be a good and practical option for areas where freshwater is limited. It is used to keep or raise lake levels, restore wetlands, and maintain river flow during hot weather or droughts, which helps protect plants and animals. Reclaimed water is also used for cleaning streets, watering parks and green spaces in cities, and industrial activities. A benefit of reclaimed water is that it provides a steady supply of water that is not affected by dry seasons or changes in weather.

Using reclaimed water reduces the amount of pollution that enters sensitive areas. It can also improve wetlands, which helps the animals and plants that live there. It also helps reduce the chance of drought because reusing water decreases the need to take water from underground sources. For example, the San Jose/Santa Clara Water Pollution Control Plant started a water recycling program to protect the natural saltwater marshes in the San Francisco Bay area.

The main risks of using reclaimed wastewater for irrigation when it is not properly treated include:

• Harmful substances, such as bacteria, viruses, and antibiotic-resistant materials, could enter the food chain.
• Soil may become too salty or contain unknown materials that could harm crops.
• Natural soil bacteria could be changed or disrupted.
• The chemical and biological makeup of soil might change, leading to the buildup of harmful substances like heavy metals, chemicals (such as boron, nitrogen, phosphorus, chloride, sodium, pesticides, and herbicides), natural chemicals (like hormones), and other emerging contaminants (such as medicines, personal care products, household chemicals, and food additives). These substances could then be taken up by plants and crops.
• Too much algae and plant growth might occur in canals carrying wastewater, leading to water pollution.
• Contaminants from reclaimed water could seep into the ground and pollute groundwater sources.

Guidelines and regulations

• World Health Organization (WHO): "Guidelines for the safe use of wastewater, excreta and greywater" (2006).
• United Nations Environment Programme (UNEP): "Guidelines for municipal wastewater reuse in the Mediterranean region" (2005).
• United Nations Water Decade Programme on Capacity Development (UNW-DPC): Proceedings on the UNWater project "Safe use of wastewater in agriculture" (2013).

Since June 26, 2023, the European Union has a regulation that sets minimum requirements for reusing water for irrigation. Water quality rules are divided into four categories based on what is being irrigated and how the irrigation is done. The water quality parameters include E. coli, BOD5, total suspended solids (TSS), turbidity, legionella, and intestinal nematodes (helminth eggs).

The Water Framework Directive mentions water reuse as one of the possible ways to meet quality goals. However, this is not a strict rule but a suggestion. Part B of Annex VI says reuse can be one of the "supplementary measures" that countries in each river basin may choose to use.

Article 12 of the Urban Wastewater Treatment Directive states that treated wastewater should be reused whenever it is appropriate. Some people say this is not specific enough because it leaves room for different interpretations of what "appropriate" means.

Although the EU does not have common water reuse rules, several member states have created their own laws, regulations, or guidelines for different water reuse purposes (e.g., Cyprus, France, Greece, Italy, and Spain).

An evaluation by the European Commission found that member states have different standards for water reuse. These differences include what uses are allowed, which parameters are monitored, and what limits are set. This lack of agreement could create trade barriers for agricultural goods irrigated with reclaimed water. If the safety standards in the producing country are not high enough, importing countries might not accept the goods. The most representative standards from European countries are:

• Cyprus: Law 106 (I) 2002 Water and Soil pollution control and associated regulations (KDP 772/2003, KDP 269/2005) (Issuing Institutions: Ministry of Agriculture, Natural resources and Environment, Water Development Department).
• France: Jorf num.0153, 4 July 2014. Order of 2014, related to the use of water from treated urban wastewater for irrigation of crops and green areas (Issuing Institutions: Ministry of Public Health, Ministry of Agriculture, Food and Fisheries, Ministry of Ecology, Energy and Sustainability).
• Greece: CMD No 145116. Measures, limits and procedures for reuse of treated wastewater (Issuing Institutions: Ministry of Environment, Energy and Climate Change).
• Italy: DM 185/2003. Technical measures for reuse of wastewater (Issuing Institutions: Ministry of Environment, Ministry of Agriculture, Ministry of Public Health).
• Portugal: NP 4434 2005. Reuse of reclaimed urban water for irrigation (Issuing Institutions: Portuguese Institute for Quality).
• Spain: RD 1620/2007. The legal framework for the reuse of treated wastewater (Issuing Institutions: Ministry of Environment, Ministry of Agriculture, Food and Fisheries, Ministry of Health).

By 2023, a new EU agriculture law may increase water reuse by six times, from 1.7 billion cubic meters to 6.6 billion cubic meters, and reduce water stress by 5%.

In the U.S., the Clean Water Act of 1972 required stopping the release of untreated waste from cities and industries to protect water for fishing and recreation. The federal government gave billions of dollars to build sewage treatment plants. Modern plants use methods like oxidation and chlorination, along with primary and secondary treatment, to meet safety standards.

Los Angeles County’s sanitation districts began using treated wastewater for landscape irrigation in parks and golf courses in 1929. The first reclaimed water facility in California was built at San Francisco’s Golden Gate Park in 1932. The Water Replenishment District of Southern California was the first groundwater agency to use recycled water for groundwater recharge in 1962.

Denver’s Direct Potable Water Reuse Demonstration Project studied the technical, scientific, and public acceptance aspects of using treated wastewater for drinking water from 1979 to 1993. A study found that the water met all health standards and was as safe as Denver’s drinking water. The cost of producing this water was also lower than getting water from distant sources.

Reclaimed water is not regulated by the U.S. Environmental Protection Agency (EPA), but the EPA created water reuse guidelines updated in 2012. These guidelines are considered the international standard for best practices in water reuse. They were developed through a partnership between the EPA, USAID, and CDM Smith. The guidelines help states create rules that follow best practices and meet local needs.

Reclaimed water is increasingly used in the U.S. for non-drinking purposes, such as watering parks, schools, highways, and golf courses; fire protection; car washing; industrial cooling; wetland restoration; and farming. In some areas, like Orange County’s Irvine Ranch Water District, reclaimed water is also used for flushing toilets.

In 2002, about 1.7 billion U.S. gallons (6,400,000 cubic meters) of water per day were reused, or nearly 3% of public water supplies. California reused 0.6 billion and Florida reused 0.5 billion U.S. gallons (1,900,000 cubic meters) per day. Twenty-five U.S. states had rules for reclaimed water use in 2002. The first reclaimed water facility in the U.S. was built at San Francisco’s Golden Gate Park in 1932. Reclaimed water is usually sent through separate pipes marked with colors to keep it away from drinking water.

• The WateReuse Association is a U.S. trade group that supports water reuse. Their website says, "The WateReuse Association is the nation’s only trade association focused on improving laws, policies, funding, and public acceptance of recycled water. WateReuse represents a group of utilities that recycle water, businesses that support recycled water projects, and people who use recycled water." The WateReuse Research Foundation was combined with the WateReuse Association on July 11, 2016.

• Canada: "Canadian guidelines for domestic reclaimed water for use in toilet and urinal flushing" (2010).
• China: China National Re

History

Wastewater reuse, whether planned or not, has been used by people for a long time. This practice is closely linked to the development of sanitation systems.

Country examples

When there are droughts in Australia, interest in using recycled water increases. Two major cities, Adelaide and Brisbane, have already decided to add recycled water to their dams, which have less water. Adelaide also built a desalination plant to help with future water shortages. Brisbane is seen as a leader in this effort, and other cities will study the Western Corridor Recycled Water Project after it is completed. Goulbourn, Canberra, Newcastle, and parts of Victoria, Australia, are already considering building systems to recycle water. Indirect potable reuse (IPR) has been discussed for communities in Goulburn, NSW, the Australian Capital Territory (ACT), and Toowoomba, Queensland.

As of 2010, Israel recycles more water than any other country. Israel treats 80% of its sewage (400 billion liters a year), and all sewage from the Tel Aviv area is reused for farming and public projects. In 2012, the Dan Region Wastewater Treatment Plant, known as Shafdan, was praised by the United Nations for using sand to naturally filter sewage. In 2010, about 400 million cubic meters of treated water were reused each year, mostly for farming. This amount makes up about 40% of the water used in agriculture.

In Namibia, recycled water is used in many cities, including Swakopmund, Walvis Bay, Tsumeb, Otjiwarongo, Okahandja, Mariental, Oranjemund, and Windhoek. In most areas, recycled water is used for irrigation. In Windhoek, recycled water is also used for drinking. Windhoek has used recycled water for 50 years. About 30% of the city’s 400,000 residents’ drinking water comes from recycled sources. A direct example of using recycled water for drinking is the New Goreangab Water Reclamation Plant (NGWRP) in Windhoek, where treated wastewater has been mixed with drinking water for over 45 years. This process uses several steps, such as ozone treatment, sand filtration, and chlorination, to ensure water safety. Since 1968, Windhoek has used recycled water as a drinking water source, which now makes up about 14% of the city’s supply. In 2001, the NGWRP was built and began providing drinking water in 2002, producing about 21,000 cubic meters of water daily.

In Singapore, recycled water is called NEWater and is bottled for special uses like education and celebrations. Most recycled water is used in high-tech industries, but some is added to reservoirs for drinking. NEWater is produced from wastewater through advanced purification. Wastewater in Singapore is treated in plants called reclamation plants. The treated water is either released into the ocean or further purified using microfiltration, reverse osmosis, and ultraviolet light.

Water recycling in Singapore was mainly driven by tensions caused by its reliance on water from Malaysia.

In South Africa, droughts are the main reason for reusing wastewater. For example, in Beaufort West, a direct wastewater reclamation plant was built in 2010 to address severe water shortages. The plant produces 2,300 cubic meters of water daily using steps like sand filtration, ultrafiltration, reverse osmosis, and ultraviolet disinfection.

In George, South Africa, the city faced water shortages and chose to use indirect potable reuse (IPR) starting in 2009/2010. Treated wastewater from the Outeniqua Water Treatment Plant is filtered and disinfected before being added to the Garden Route Dam, increasing the city’s water supply by 10,000 cubic meters daily. This meets about one-third of the city’s drinking water needs. The process includes steps like screening, ultrafiltration, and chlorine disinfection. Additional steps, such as adding powdered activated carbon, are available if needed.