A sign in drought-tolerant landscaping stating that reclaimed water is used for irrigation

When water levels dropped last year, waterways like the Mississippi River and Lake Mead became shallower than children’s pools. although extreme drought as of 2022 has declined in many places, 28 percent of the continental US is still experiencing drier than average conditions.

Both Lake Mead and the Mississippi River serve as freshwater sources for nearby communities. The threat of drought has prompted many municipalities to consider how wastewater can be reused, and the recent Bipartisan Infrastructure Act earmarked funding for communities looking to recycle water and become more drought resilient.

Emergency water transfers have supplemented dangerously low supplies in some drought-stricken cities such as Coalinga in Central California. In these arid regions, water recycling can help end future shortages.

Read more: How old is the water we drink?

Types of water 101

Water is generally divided into three categories: potable, black and grey.

Drinking water is purified drinking water that is piped to homes. People use this water in their showers, sinks, toilets, washing machines and dishwashers. The wastewater is then returned through a main line back into the sewer system.

Most municipalities there is one line to send wastewater back into the system and the system does not differentiate between a dirty gallon flushed down the toilet and reusable water from the washing machine. Problematically, the majority of domestic wastewater is reusable and can be repurposed as non-potable water.

According to local regulationsnon-potable water can be direct pipeline in irrigation systems and is used to water lawns and gardens. It can also be used for outdoor cleaning, such as washing a car or scrubbing a patio. Systems can also be developed so that water is captured, treated and used for service toilets or laundries.

However, water recycling systems must be carefully designed to keep contaminated and non-potable water separate to avoid the spread of harmful chemicals and deadly bacteria.

Blackwater vs. Greywater

Black water is contaminated water that is flushed down the toilet. Depending on the municipality, the water thrown out of the dishwasher can also be considered black. Gray water comes from sinks, showers and washing machines.

Gray water usually has one tenth of the nitrogen content from black water. Nitrogen is a dangerous pollutant and a difficult chemical to manage during the reclamation process. Gray water also does not have the same pathogens found in black water, which comes from human waste.

Gray water does have its common contaminants. 2020 survey in International Journal of Chemical Research examined gray water from residential buildings and found that it contained heavy metals as well as compounds such as nitrates and phosphates. The authors suggest that the contaminants come from cosmetics, body lotions, and hair dye. They concluded that greywater must be treated before it can be consumed, but can be used for other domestic purposes.

Using Greywater

Greywater reclamation can have a major impact on water supplies, especially in drought-prone areas. Between 60 and 75 percent of household waste water is gray water, and of this, 50 percent is considered “light gray,” meaning there aren’t as many contaminants that require treatment.

When greywater is used instead of potable water for flushing toilets, watering lawns and washing cars, the demand for fresh water supplies can drop between 26 to 41 percent. Creating a reuse system requires investment from municipalities so that gray water can be sent for reclamation separately from black water. In addition, a water supply system is needed that differentiates between potable water sent to sinks and gray water piped to toilets.

Although it would be nice to send the water from the sink directly to fill the toilet, raw gray water cannot be used indoors because it can quickly develop bacteria that can be harmful to humans.

Untreated greywater can be used directly outside, which can be a relief in drought-prone areas.

Some cities in California are now allowing people to create an irrigation system that takes the water from their washing machines and reuses it to irrigate their lawns and gardens. The irrigation system should usually be professionally installed to avoid crossing gray and potable water lines.

Gray water it is not recommended for use on garden fruits or vegetables. It is also not recommended for plants that prefer acidic soil.

Although it cannot be used everywhere, it can make a big difference in reducing water. The average American household uses about 50 gallons of water in their washing machines every day. A redesigned system can stop both water and steam from disappearing down the drain.

Read more: Why lakes are important resources

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