While recycled water reuse has been steadily increasing in California since 1970, a task force in 2003 found that water reuse could potentially increase another 1.4 to 1.7 MAF.
Facing ongoing drought and growing water demand, many communities are turning to recycled water as a way to develop reliable local water resources. By building advanced water treatment facilities to extract pure water from sewage effluent, it is possible to create a sustainable water supply that is cheaper than desalinating seawater or buying new imported water supplies.
Decades ago, attempts to build recycled water projects in Southern California were given the distasteful moniker ‘toilet to tap’ and subsequently met with strong public disapproval. But the truth is oftentimes the water we drink now has already been recycled as in many cases, the water withdrawn from rivers and streams for a community’s drinking water source contains discharged water from a wastewater treatment plant upstream.
WHAT IS RECYCLED WATER?
Recycled water is highly-treated wastewater that has undergone multiple levels of treatment to meet stringent quality and safety standards set by the State Water Resources Control Board. Treatment typically consists of filtration to remove suspended solids, some bacteria, and other pollutants; disinfection is then used to destroy any remaining bacteria and viruses. This water can then be used for landscape or agricultural irrigation, commercial applications such as car washes, or industrial processes such as cooling towers. With further treatment, it can even be used as a potable water supply.
There are three levels of wastewater treatment:
- Primary treatment is usually the first stage of wastewater treatment, and is designed to remove suspended and floating solids from raw sewage.
- Secondary treatment uses biological processes to remove dissolved organic matter by using microbes which consume the organic matter. Secondary treatment includes the basic activated sludge process, pond and constructed wetland systems, and trickling filters and other forms of treatment which use biological activity to break down organic matter.
- Tertiary treatment is the most stringent, going beyond secondary treatment to remove more than 99% of the impurities. The treatment removes remaining inorganic compounds and substances, such as nitrogen, phosphorus, bacteria, viruses and parasites. It is the final cleaning process that improves wastewater quality before it is reused, recycled or discharged to the environment.
USING RECYCLED WATER
Recycled water can be used through either unplanned uses or by specific planned projects. Unplanned reuse occurs when the treated wastewater is discharged into a surface water body and flows downstream where it can benefit wetland or aquatic habitat or be withdrawn for municipal use. Planned use occurs when projects are developed for specific uses such as landscape irrigation, agricultural irrigation, or industrial purposes.
Recycled water treated to the highest standards can augment water supplies by using it to recharge groundwater aquifers or by putting it into surface water reservoirs that are used for drinking water supply.
Direct potable reuse would occur by putting highly treated wastewater directly into drinking water supply lines. It is not currently happening in California, but the process to develop regulations to do so is currently underway at the State Water Board.
THE POTENTIAL OF RECYCLED WATER
Water recycling has been steadily increasing since 1970, but more can be done. In 2003, the Recycled Water Task Force estimated that 1.4 to 1.7 MAF could be recycled annually. Of that, 0.9 to 1.4 MAF could be realized through recycling water that is discharged into the ocean or brackish bays, thereby capturing municipal wastewater that would otherwise be irrecoverable and generating ‘new’ supplies.
A survey in 2015 found California reused 714,000 acre-feet of municipal recycled water, an increase of 45,000 AF since the last survey in 2009. However, the survey was conducted during the drought when mandatory water restrictions were in place and flows to wastewater treatments plants were reduced. Significant increases are expected in the next few years as projects that received Prop 1 or 2014 Drought Grant funding are completed and go online.
BENEFITS OF RECYCLED WATER
Recycled water can be a reliable, local source of supply. Municipal recycled water is considered somewhat drought-resistant as municipal wastewater will still occur, even during droughts. Recycled water can also aid in climate change adaptation as it is less sensitive to temperature and precipitation changes.
In some cases, recycled water can provide energy savings when compared to the energy used for importing water from long distances or for seawater or brackish desalination; however, recycled water for most urban applications requires tertiary treatment, which requires a significant amount of energy to produce.
COSTS OF RECYCLED WATER
The costs of recycled water projects depend on the amount of water to be treated, treatment requirements, infrastructure needs, project planning, permitting, and financing, so costs do vary; generally recycled water costs can range from $300 to $1300 an acre-foot, sometimes higher.
A significant cost component of recycled water is the distribution systems that are needed to expand its use. Since current regulations prohibit conveying recycled water and potable water in the same pipelines, a separate purple pipe system must be installed. Consequently, extending purple pipe systems to users near treatment plans can be more cost-effective than extending purple pipe systems to those users farther away.
There are many issues involved in implementing recycled water projects:
- Costs and affordability are often an issue. A common reference point is what is currently paid for water sources versus what will have to be paid for in the future for new water supplies. However, some benefits are hard to quantify, such as the value of having a reliable source of water during droughts. And while technological advancements in water recycling technology are likely to occur in the future that could reduce costs, dedicated recycled water distribution systems will remain costly.
- Public acceptance for recycled water is critical to the project’s success. Generally, there is public acceptance and support for non-potable applications, such as agricultural or landscape irrigation. Acceptance can be harder to achieve for projects with direct links between recycled water and human consumption or contact; however, outreach and education programs during the planning phases can provide the public reassurance and bolster support.
- Recycled water can result in a reduction of the volume of water discharged into streams or rivers. This can adversely affect downstream users or instream beneficial uses.
ON-SITE WATER RECYCLING
Increasingly, water is being recycled and reused on-site, from small scale greywater systems in homes to entire buildings that are cleaning and reusing water.
According to the EPA, the average American family of four generates about 200 gallons of water a day that’s considered greywater, which is water from bathroom sinks, showers, tubs, and washing machines. The benefits of grey water recycling include lower potable water use, less strain on septic tanks or treatment plants, less energy and chemical use, groundwater recharge, plant growth, and reclamation of otherwise wasted nutrients. Greywater systems provide better treatment for the wastewater because topsoil is many times more effective than a treatment plant.
While greywater may contain traces of dirt, food, grease, hair, and certain household cleaning products, it can safely be used for landscape irrigation. However, using a greywater system often requires changing bath soap, shampoo, and laundry soap to versions that don’t have chemicals that could pollute the groundwater.
Dense, urban centers are also looking to the use of on-site alternate water sources as a key strategy for developing alternative, regional supplies. Buildings themselves can be designed to capture and reuse grey water and blackwater, as well as rainwater collected from rooftops and other runoff from the landscape. This water can then be used for toilet and urinal flushing, cooling towers, and landscape irrigation. In September 2012, the City and County of San Francisco adopted the Onsite Water Reuse for Commercial, Multi-family, and Mixed Use Development Ordinance which allows for the collection, treatment, and use of alternate water sources for on-site non-potable applications. The ordinance further mandates that all new development projects of 250,000 square feet or more must install onsite water systems to treat and reuse available alternate water sources. For more on San Francisco’s Non Potable Water Program, click here.
FOR MORE INFORMATION
Helpful documents and websites …
- Water recycling and reuse: The environmental benefits, webpage from the US Environmental Protection Agency
- San Francisco’s Non Potable Water Program, from the San Francisco Public Utilities Commission
State agencies working with recycled water …
- Recycled Water Policy page, webpage from the State Water Resources Control Board
- Division of Drinking Water’s Recycled Water Information, webpage from the State Water Resources Control Board
- Direct Potable Reuse, webpage from the State Water Resources Control Board