Recycled Water

All the water that was or ever will be on earth is here right now and is over 4 billion years old. More than 97% of the Earth’s water is within the in oceans. The remaining 2.8% of water is the fresh water that is within the land masses.  

Of that fresh water- 77%  is estimated to be in icecaps and glaciers (melting away as the planet warms) and the remaining fresh water is stored primarily in the subsurface as ground water. The tiny fraction of a percent of water that remains are the rivers and lakes that supplies the lion’s share of mankind’s needs. River and lakes are repeatedly renewed by rainfall. Rain drops fall to earth and evaporate, infiltrate into the soil, recharge groundwater or flow along the ground to a stream and ultimately flow into rivers and to the ocean-moving always moving.

 As average temperatures at the Earth’s surface rise, more evaporation occurs, which, in turn, should increase overall precipitation. Therefore, a warming climate is expected to increase precipitation in many areas, but not all.

According to NASA: “Current climate models indicate that rising temperatures will intensify the Earth’s water cycle, increasing evaporation. Increased evaporation will result in more frequent and intense storms; but will also contribute to drying over some land areas. As a result, storm-affected areas are likely to experience increases in precipitation and increased risk of flooding, while areas located far away from storm tracks are likely to experience less precipitation and increased risk of drought.”

We are past the point where we can try to stop or reverse climate change and hope the climate will return to what it had been. Precipitation will not continue to fall in the patterns of the past. According to the U.S. EPA:  On average, total annual precipitation has increased over land areas in the United States. However, a few areas, such as the Southwest, have seen a decrease in precipitation.  

A mix of growing population, economic growth and changes in precipitation patterns has created a severe water shortage in California that could grow into a crisis in the near future. As drinking water sources become more scarce, California and other states look to directly recycle wastewater to drinking water. Potable reuse systems are up and running around the United States. The Orange County Water District has run the world’s largest water recycling plant since the 1970s. Water providers in Northern Virginia, Atlanta, Georgia, and Aurora, Colorado, also use potable reuse water as part of their drinking water supplies.

Potable reuse, the process of treating wastewater to drinkable standards, offers a reliable and sustainable solution to cities and regions facing shortages of clean water. The city of Los Angeles and water agencies across Southern California are looking into what’s known as “direct potable reuse,” which means putting purified recycled water directly back into our drinking water systems.  What was once called toilet to tap recycling. This differs from the indirect potable reuse we have here, where water spends time in our Occoquan reservoir.

Los Angeles plans to recycle all of its wastewater by 2035 and the California State Water Resources Control Board has been tasked by legislators with  developing a set of uniform regulations on direct potable reuse by Dec. 31, 2023. Meanwhile, a direct potable reuse demonstration facility near Griffith Park will serve to demonstrate the concept.

To accomplish that, the Hyperion Water Reclamation Plant — which like all wastewater treatment plants currently treats wastewater only to the level necessary for release— must be converted into an advanced water purification facility that produces water clean enough to drink.

To complement these plans, a group at Stanford University have be studying the quality of reclaimed water. They expected that potable reuse waters would be cleaner, in some cases, than conventional drinking water due to the fact that much more extensive treatment is conducted for them,” said Stanford professor William Mitch in a new study published in Nature Sustainability.  Toxicological assessment of potable reuse and conventional drinking waters | Nature Sustainability

The engineers found that, after treatment, potable reuse water is cleaner than conventional drinking water sourced from pristine-looking rivers. In most rivers, somewhere upstream is wastewater and stormwater releases  which have much less treatment than occurs in potable reuse systems.

Regulators demand more extensive treatment at potable reuse treatment plants. They specify that treatment systems must remove harmful pathogens, such as viruses and amoebas, and utilities flush out other contaminants using reverse osmosis, ozonation, biofiltration, and other cleaning techniques.

Reverse osmosis treatment pushes water at high pressure through a filter that's so small, it is the method of desalinization. Dr. Mitch and his colleagues discovered the process cleans wastewater as much if not more than groundwater, which is the gold standard. Even when reverse osmosis wasn’t applied, reuse waters were less toxic than the samples of conventional drinking waters sourced from rivers across the United States.

Conventional wastewater treatment plants just aren’t equipped to deep clean. This leaves many organic contaminants, such as chemicals from shampoos and medicines and trace contaminants from our manufactured products, floating down river and straight into a drinking water plant. Direct potable reuse will require building the water treatment plants to remove all these contaminants. Los Angeles is estimating $16 billion to implement these upgrades. However, California is not known for reliable cost estimates for big projects. 

Read the full study: Lau, S.S., Bokenkamp, K., Tecza, A. et al. Toxicological assessment of potable reuse and conventional drinking waters. Nat Sustain (2022). https://doi.org/10.1038/s41893-022-00985-7.