Treating Greywater Cost Effectively While Protecting the Public’s Health

Concerns over reduced fresh water resources dry climates and overloaded and costly wastewater treatment facilities have forced utilities to look at water management from two very important perspectives: efficiency and conservation. An approach that has been gaining interest is the reuse of greywater (or, graywater) for toilet flushing and irrigation. Greywater is wastewater from lavatory sinks, showers, bathtubs and laundry machines, and excludes water from dishwashers, kitchen sinks and toilets. Greywater constitutes between 50 – 80% of domestic water consumption, and can be reused for toilet flushing or irrigation with simple treatment to reduce the stress on natural water systems (Gross et al. 2007). In addition, the characteristically low organic content of greywater renders it suitable for non-potable applications with minimal treatment (Pidou, 2006). Not surprisingly, greywater reuse has been common in the U.S. for the past decade. The Water Conservation Alliance of Southern Arizona conducted a study in 2000 that showed 13% of homes were reusing greywater for non-potable applications.

Although the components of greywater quality have been well documented, health risks as a result of recycling greywater are still unclear. Furthermore, risks vary depending upon exposure (toilet flushing or irrigation) and scale (residential versus commercial) (Dixon et al., 1999).  Pathogens, viruses and the contents in personal care products constitute the concerns when the end use of greywater recycling is irrigation. When toilet flushing is the end use of treated greywater, the primary concern is the presence of pathogens and viruses due to the potential of greywater contacting humans. Although Arizona and California are the leaders in enhancing greywater reuse, these states have adopted different approaches when it comes to permitting and regulating greywater systems. For example, Arizona does not require a permit for greywater reuse for systems with a capacity of less than 400 gallons per day. California does require a permit for all greywater installations (except for washing machine applications) and has adopted strict installation requirements. The differing approaches, varying risks relating to end use or system size have all added to the difficulty of developing greywater reuse standards and made it difficult for some regulatory bodies to set guidelines that encourage greywater reuse.

Although it is possible to treat greywater to a drinkable (potable) quality it is a rare practice due to regulatory restrictions and cost of treatment required. The alternative is to treat greywater for non-potable uses such as:

• greywater reuse for individual household irrigation
• greywater reuse for individual household toilet flushing
• greywater reuse for commercial buildings or multifamily irrigation
• greywater reuse for commercial buildings or multifamily toilet flushing

If the intended end use for greywater is toilet flushing, the system must utilize a form of disinfection to meet regional regulatory requirements. Furthermore, it is widely agreed that greywater should be disinfected prior to reuse for flushing toilets (U.S. EPA, 2010). Advanced treatment very often means more maintenance and increased cost. The options available include filtration and disinfection systems, treatment wetlands, biological treatment and reverse osmosis. Filtration and disinfection systems tend to be the most cost effective and set out to meet the minimum plumbing code requirements. As a result of having to clean filters and add disinfectant, the maintenance requirement of these systems is straightforward and simple. Although filtration and disinfection systems can be effective in treating indicator organisms (fecal coliform) they do not always achieve high water quality with respect to the organics in greywater (BOD, TSS and Turbidity).  Therefore, if regulations require a strict BOD and TSS levels, filtration and disinfection may NOT be sufficient and biological treatment may be necessary. Biological treatment such as sequencing batch reactors, membrane bioreactors and biological aerated filters are capable of treating greywater to a high quality (< 20 mg/l BOD, <20 mg/l TSS, and <10 cfu/100ml E.coli). Essentially, these systems act as small waste water treatment facilities, capable of treating waste water. However, biological systems are expensive and operating and energy costs are higher. The question that is highly debated is whether or not greywater reuse for non-potable purposes should require that high level of treatment and expense to truly protect public health.

There are 20 states that allow a form of greywater reuse, and not surprisingly the regulations adopted vary state by state.  Greywater regulations follow varying codes with the two most common being plumbing and health codes. Many states have adopted a plumbing code such as the Uniform Plumbing Code (UPC), the International Plumbing Code (IPC) or the National Standards Plumbing Code which have created protocols for implementing greywater systems. When there are any discrepancies between the plumbing code and Health Department laws precedence tends to be given to the Health Department. Additionally, local regulators such as cities or counties may enforce stricter or easier greywater regulations compared to state codes.

The comparison that follows is meant to provide a broad overview of greywater regulations in the United States and is meant to provide a general overview. As rules and regulations changes over time, one should always contact their regional regulatory bodies for the latest and current information regarding water reuse legislation and permitting requirements.