How Water Reuse Can Address Scarcity

Only 3% of Earth’s water is considered freshwater. Only 0.5% is readily available for humans. Freshwater is essential for human survival—for our drinking water, of course, but also to support ecosystems and enable key sectors of the economy such as agriculture to energy production. In the midst of climate change, freshwater resources are becoming increasingly scarce. Irregular rainfall and droughts diminish water supplies, while rising temperatures increase evaporation and evapotranspiration rates from lakes and rivers, further reducing available water. Additionally, the melting of glaciers, which serve as critical freshwater reservoirs and significantly contribute to downstream river flow, threatens long-term water availability for many regions, especially Arctic and sub-Arctic regions such as Alaska.

Given these challenges, water reuse can play a vital role in preserving our freshwater resources. Water reuse, or water recycling, is the process of treating and repurposing wastewater for applications such as irrigation, industrial processes, and even household uses such as bathing, cooking, and drinking. By promoting the conservation of freshwater sources, water reuse can help address the impacts of climate change on our water supply.

Types of Water Reuse

Water reuse can be tailored to the specific needs and resources of a community or region. Potable water reuse involves heavily treating wastewater from residential and commercial sources and sometimes blending it with other water supplies, such as surface and ground waters, to ensure safe and reliable drinking water. There are two types of potable water reuse:

• Indirect potable reuse: Wastewater is treated at a wastewater treatment facility then pumped into a natural basin or reservoir where it is filtered naturally through the ground before being sent back into the water supply.
• Direct potable reuse (or purified water reuse): Wastewater undergoes advanced treatment processes so it can be delivered immediately to the drinking water supply system without the need for an environmental buffer.

Non-potable water reuse, also known as water reclamation, recycles wastewater for uses that do not require the rigorous treatments necessary for drinking water standards. Common uses for reclaimed water include irrigation, industrial processes, and toilet flushing. Treating water to meet drinking standards requires significant energy use, but non-potable water reuse allows for a less intensive treatment process, lessening strains on energy resources.

A specific type of non-potable reuse is graywater reuse, which involves repurposing water from sinks, showers, and washing machines within the same building or property. This water is used again for applications like irrigation and toilet flushing without undergoing treatment elsewhere. It is important to note that graywater excludes wastewater from toilets, kitchen sinks, and dishwashers. These types of water are classified as blackwater, due to higher levels of organic contamination, and are not suitable for the environmentally beneficial uses associated with greywater since blackwater requires additional treatment to be safe for reuse. Graywater reuse reduces demand on freshwater sources such as rivers and lakes by providing alternative sources for non-potable uses.

Water Reuse Across the United States

More than half of U.S. states have already implemented policies regulating water reuse, with the strongest initiatives found in the West, where water scarcity is a chronic issue. The Los Angeles County Sanitation Districts operate one of the largest wastewater recycling programs in the world, providing affordable recycled water to over five million people. The Los Angeles Department of Water has implemented a Water Conservation Ordinance which has been instrumental in decreasing wastewater flows. These actions, alongside the promotion of other conservation initiatives by the county, have allowed the Sanitation Districts to streamline their focus to stormwater diversion as an alternative water source. To date, over 14 stormwater diversion projects have been established, diverting an average of nearly 439,000 gallons of stormwater per rainy day into the sewer system. Once the stormwater enters the sewer system, it is distributed to one of 11 wastewater treatment plants to be treated for non-potable and indirect potable reuse. These projects are funded by the