When it comes to recycling, people often think of materials such as aluminum cans or plastic bottles. But did you know that water can also be recycled?
In the US and other developed countries, we generally turn on the faucet, use the water, and then let it flow down the drain and into the sewage system. This wastewater is eventually treated and released into rivers or the ocean. Many advocates of water recycling see this as a waste, especially considering how precious water is—just 1% of the water on Earth is available for human use. Rather than using water only once, we can purify wastewater and use it again before discharging it back into the environment.
Driven by droughts, population growth, and the depletion of underground aquifers, a number of communities around the world have turned to water recycling as freshwater supplies shrink. This problem is increasingly widespread. The UN has warned that half of the world’s population will face water scarcity by 2030.
In many cases, water recycling can provide a significant new source of water for communities to use. For example, in California, the state Department of Water Resources estimated that recycled water could provide an additional 1.8 to 2.3 million acre-feet of water per year by 2030. (For reference, an acre-foot is the amount of water needed to cover 1 acre of land in 1 foot of water.)
Following is a guide to everything you need to know about water recycling and reuse.
Most commonly, people use recycled water for non-potable, or non-drinking, purposes. This includes activities such as watering agricultural crops, outdoor landscaping, and golf courses. Other non-potable uses for recycled water include toilet and urinal flushing. Recycled water can also be employed to cool power plants and oil refineries, as well as in paper mills or other types of factories. At construction sites, recycled water can be used to mix concrete and curb dust, as well as for other purposes.
Some recycled water can be used for potable (or drinking) purposes, although it’s not as simple as purifying wastewater and sending it directly back into homes and businesses. Most often, the recycled water is used indirectly. For example, a city may treat and purify its wastewater, then inject it into underground wells to boost groundwater supplies or to prevent saltwater from seeping into the groundwater in coastal areas. This is known as indirect potable reuse.
The largest indirect potable reuse system in the world is located in Orange County, California. The Groundwater Replenishment System there takes wastewater that would otherwise have been released into the Pacific Ocean, purifies it, and pumps it into percolation basins. There, the recycled water naturally seeps down through the gravel and sand, eventually reaching—and adding to—the underground aquifer that cities use for drinking water.
Direct potable reuse, which involves adding recycled water directly to the drinking water supply, is less common. In the US, the city of Big Spring, Texas, was the first to build a direct potable reuse system. The facility treats wastewater with microfiltration, reverse osmosis, and ultraviolet disinfection, then mixes it with conventional water supplies. The resulting mixture is treated again to meet drinking water standards.
Greywater and blackwater
Besides non-potable and potable uses, recycled water can also be described in terms of greywater or blackwater. Blackwater is wastewater from toilets, while greywater refers to wastewater from sinks, showers, baths, dishwashers, and washing machines. Since it’s not contaminated with urine or fecal matter, greywater is easier to treat and reuse. In some cases, people can even use greywater for non-potable purposes without any kind of chemical or UV treatment.
An at-home greywater system can be as simple as using a bucket to collect water in the shower while it warms up, then to water the garden. A more advanced “laundry to landscape” system might include a pipe with switchable valves leading from the washing machine outdoors into the garden. With this kind of system, it’s necessary to use non-toxic and biodegradable soaps. Those interested in installing a greywater system should check with their city or local government to learn the applicable rules and regulations.
Decentralized and centralized water recycling systems
The do-it-yourself, at-home greywater recycling systems are fundamental examples of “decentralized” systems, because they collect and reuse water on-site. In comparison, the municipal plants in Big Spring and Orange County are centralized water recycling systems because they collect and treat wastewater from a wide area, and the resulting purified water is eventually distributed over a similarly large area.
The city of San Francisco, California, is a leader in decentralized water recycling. In 2015, the Board of Supervisors passed a law requiring new developments larger than 250,000 square feet to include on-site water recycling systems. These systems will collect and treat greywater for non-potable purposes such as flushing toilets and urinals, as well as watering outside landscaping. With these new regulations, the city became the first in the country to require on-site water recycling in new buildings.