Reliable DPR

Uncertain Water Supply

Less than three percent of the Earth’s water is freshwater, and only 30 percent of freshwater is groundwater, with the rest stored in glaciers and ice caps. Less than .3 percent exists as surface water in rivers, lakes and streams. That’s right – just .3 percent is surface water. Freshwater is an invaluable and sometimes scarce resource. Most of our daily drinking water comes from surface water. Yet, in the United States, we take this for granted. Treated drinking water is used for all household water, including toilets. This valuable resource is literally flushed down our drains. We water our lawns with drinking water. We shower with drinking water. We use drinking water in industrial manufacturing and agriculture. With a rising number of serious droughts in the Western states, it is increasingly clear that we need to rethink how we use our limited water resources.

Water Reuse Strategies

There are many ways to reuse water that can help relieve the burden on shrinking reservoirs and reduced ground water supply. We need solutions to make our water sources more reliable. In the context of water reuse, reliable means robust, resilient, redundant and low risk.

• We need systems that are robust enough to handle varying water supply demands.
• They must be resilient enough to bounce back quickly when unusual conditions occur.
• We need systems that have enough redundancy to protect public health.• And, we need to contain risk at all levels to ensure a stable, safe water supply.

We need to be able to trust our household water sources.

Of the strategies available to help meet water demands, there are two basic alternatives. One is focused on the consumer side, with strategies for water conservation that can be performed by individuals and households without any changes to the water supply or distribution systems. These consumer side strategies range from the very simple—using less water, taking fewer showers, watering the lawn less frequently, etc.—to the complex. Greywater reuse and greywater systems are an increasingly popular means of reducing water demand for individual households

Greywater Reuse

According to the Environmental Protection Agency (EPA), the average American household of four uses around 400 gallons of water a day, not counting water used for the lawn. Greywater systems take used household water from sinks, showers, washing machines and other household sources and store them for non-potable uses around the home. If non-toxic, biodegradable soaps are used, this water can be repurposed for irrigation of yards and gardens. Water from the toilet, one of the main uses of household water, cannot be used for greywater, due to the pathogens in waste. Since toilet flushing accounts for a large quantity of household use, up to 27 percent of older toilets are in place, and since there is a limit to the amount of water needed by lawns and gardens, greywater cannot provide a comprehensive water reuse system. Along with water conservation strategies such as low flow toilets, it can help reduce water demand significantly. Although estimates vary depending on water use in different regions, greywater systems can generally save around 30 percent of household water use.

Local regulations create major barriers that restrict the use of greywater systems. Not all states have greywater regulations (which can make it difficult to get approval to install greywater systems), and those that do may require permits to ensure public safety. In Arizona, for example, greywater is allowed only where groundwater is at least five feet below ground level, and where water will not run off onto neighboring property. Only drip or flood irrigation is allowed, and greywater cannot be used to irrigate food producing plants other than citrus and nut trees. In addition, greywater requires changing cleaning supplies to ensure they will not damage the environment. A greywater system may also be expensive, depending on how extensive it is.

Recycled Water

More systematic water reuse must be tackled by community, commercial and industrial water systems. For example, recycled water at the system level is treated at a high level to remove pathogenic materials. Recycled water often exceeds drinking water standards, but is not allowed for potable use. Recycled water is identified by separate lavender colored plumbing and piping to indicate it is unsuitable for drinking. Recycled water has the advantage of saving money for commercial and industrial water customers who can gain a more reliable source of quality water for use in agriculture and manufacturing. Recycled water is used for agricultural irrigation, landscape irrigation, groundwater recharge, construction use, industrial use, and many other uses such as commercial and domestic toilet flushing where separate plumbing is available. Recycled water may also be discharged to surface waters where permitted.

Recycled water provides a local source of water for non-potable purposes, reducing the cost of treating and transporting water associated with drinking water treatment. It can reduce demand for potable water, and prevent the use of potable water for irrigation. However, using recycled water for toilet flushing and other non-potable uses may require dual plumbing to keep potable and non-potable water separate. The costs associated with installing a second set of water conveyance lines is a barrier to making full use of recycled water. In some cases, more treated water is produced than can effectively be used in irrigation, meaning high-quality water is wasted.

Indirect Potable Reuse

Indirect potable reuse (IPR) helps reclaim more water than recycled water. Indirect potable reuse generally adds an additional treatment step to ensure water is free from pathogens before sending it to an environmental buffer like wetlands, groundwater recharge or surface waters to augment the drinking water supply. This water is eventually pumped out of lakes, reservoirs or aquifers after natural processes have further purified it. Ultraviolet light from the sun, for example, is an excellent natural purifier that helps breakdown unwanted contaminants in treated water.

Accidental indirect potable reuse is common, as water treated at a wastewater facility and discharged to a river or stream may provide the source of drinking water to a downstream community. In effect, people have been indirectly recycling water for a long time, but planned projects to do so may meet with resistance from the public if proper education is not in place. The initial distaste at the concept of drinking wastewater can overcome the rational understanding that all water is recycled water.

In the U.S., California has more than 40 years of experience with IPR and leads the country with the most IPR projects. Orange County’s Groundwater Replenishment System (GWRS) is the world’s largest IPR system. Orange County has been using IPR since 1975 when Water Factory 21 came online. This facility blended treated wastewater with deep well water and injected into groundwater basin to prevent seawater intrusion. Water Factory 21 was closed down in 2004 and replaced by GWRS in 2008.

Direct Potable Reuse

Direct Potable Reuse (DPR) has a bad rap. It is often denigrated as “toilet to tap” water, and has had the most difficulty achieving public acceptance. What DPR projects do is to remove the environmental buffer and replace it with an engineered buffer. This might not seem like a big difference, but it enables closer control of the process, and reduces the amount of piping and pumping required to reuse the water. Water is treated and disinfected at the wastewater treatment facility using state-of-the-art advanced water treatment technologies. It is then stored—to provide additional control over water quality—before being blended with raw water, or introduced directly into a water treatment or distribution system. This treated water is, in many ways, superior to raw water—contaminants are present in vanishingly small quantities compared to raw water.

Direct potable reuse is, dollar for dollar, one of the best alternatives available for water conservation and reuse. DPR may not be suited to every situation, but in very dry areas it helps control evaporation. It doesn’t require the capital investment of recycled water piping and plumbing, and it reduces the energy required to pump water to and from environmental buffers such as lakes and streams. If it is properly implemented, it is entirely safe.

DPR is not new—Windhoek, Namibia has been using direct potable reuse since 1968. Windhoek is in one of the driest regions of the world, and has had to find innovative means of suppling water to its 325,000 residents. New Goreangab Water Reclamation Plant treats wastewater and produces almost 25 percent of Windhoek’s 15 million gallon-per-day demand for water.

The Texas drought that began in 2010 was one of the driest recorded. When the drought broke, it didn’t end everywhere. Some parts of Texas remained in drought even as the rest of the state experienced relief. River beds ran dry, local residents prayed for rain and water rationing was the norm. In Wichita Falls and Big Spring, DPR projects were initiated to mitigate the continued dearth of water. These DPR projects do not use environmental buffers, and treated water is blended with raw water before being treated again at the water treatment facility and distributed to the public.

Singapore’s NEWater Initiative is an attempt to reduce dependency on imported water from Malaysia. Using technologies adopted from U.S. reclaimed water strategies, Singapore provides high-quality reclaimed water primarily to industry. This water contains fewer impurities than are allowed for drinking water. In dry periods, Singapore’s reclaimed water can be blended with raw water in reservoirs to augment supplies of drinking water.

Reliability is Key

As recycled water, IPR and DPR projects become increasingly common in drought stricken or extremely dry areas, reliability becomes increasingly necessary. In order for the public to accept projects that have public health risks, they must believe that these risks are very low. While recycled water and IPR have environmental buffers that decrease the impact of potential contaminants, DPR absolutely requires reliable programs be in place to safeguard public health.

When talking about reliability and DPR, most people think about the design. Going back to the definition of reliability: is it resilient and robust, and does it have adequate redundancy to reduce the risk of failure at any point in the process before contaminants enter the drinking water supply? But as important as these questions are, it is equally important to have a reliable operation and maintenance program to support consistent treatment. A state-of the art, technologically sophisticated plant will only function as well as its operations program. A $2B facility may depend on the effectiveness of a $50k/year employee.

Reliability Centered Maintenance (RCM) offers that security for increasingly complex operations. RCM is widespread in industries that have high risk of public harm, such as the airline, nuclear power and chemical processing industries. Using RCM could help allay public fears and health concerns while providing the structure to maintain reliable, safe, low-risk operations. DPR provides the innovation, but RCM provides the game plan and guides long-term safety and performance. DPR projects have a higher than average responsibility to protect the public, and cannot operate in a reactionary mode. It is critical to have a proactive, risk-based approach to operations and maintenance. RCM identifies hidden failures, and helps develop operator response corrective actions well before a crisis hits. By identifying the most critical equipment and processes, RCM helps O&M staff and management determine where to focus efforts to ensure sustainability of the process.

RCM offers advantages to operations and maintenance programs at all facilities, but it is especially vital at facilities that carry public health risks. Best-in-class operations and maintenance practices are required when dealing with reuse of wastewater.