by Nick Gromicko, CMI®
"Greywater" (also spelled graywater) is wastewater collected from household showers, sinks, tubs and washing machines that would otherwise be sent down the drain and into the sewage
system. Greywater is not potable water, but it can be used for some household activities such as flushing toilets and, more commonly, for irrigation. Greywater differs from "blackwater," which is water that has come into contact with fecal matter or people who carry infectious diseases.
There are two main classifications for greywater:
- Untreated greywater is collected relatively cheaply and is always used immediately. It may be utilized for flushing toilets or for outdoor irrigation, where it is then purified by plant roots and soil life.
- Treated greywater is collected using automated diversion, purification, and irrigation systems, which render greywater suitable for storage and for additional uses, such as for washing and laundry.
Adversaries of greywater usage cite concerns that greywater systems could harbor and spread disease. Proponents of greywater systems acknowledge that much household water usage does not actually require potable water, and that greywater systems, when implemented properly, provide an important secondary source of household water.
Facts and Figures
- According to Oasis Design, “The total number of households utilizing greywater is estimated to range from 660,000 to 1.77 million in California, and to reach 8 million in the United States." In 2009, Oregon passed a law that encourages the use of greywater.
- Although there is no comprehensive study on the public health risks of greywater, there have been no reported cases of illness from contact with greywater in the United States.
- Greywater usage is common and often not regulated in many Third-World nations.
- All greywater has the potential to harbor dangerous bacteria and viruses.
- It is never potable.
- Micro-organisms present in untreated greywater can cause damage to foliage.
- Untreated greywater should not be used for lawn sprinklers, as this could spread dangerous, airborne bacteria.
- Greywater that is not able to permeate down into the soil can create pools that may leach out and contaminate neighboring surface waters.
- Harsh detergents from laundry and washing water, such as dyes, bleaches and bath salts, may have a negative impact on vegetation.
- High levels of fats and food residue from kitchen waste may block plumbing.
- Accidental cross-contamination of pipes can lead to drinking-water contamination. Only a licensed plumber should implement changes to existing plumbing structures.
- Irrigating too close to a private well could lead to contamination of the drinking water supply.
- Emptying untreated greywater into a toilet's tank may cause a foul odor; when flushing with greywater, pour it directly into the toilet bowl.
Adavantages to Greywater
- Implementing greywater systems may result in a substantial cost savings, both in fresh water and sewage costs.
- Using greywater lessens stress on municipal sewage systems and water supplies, which is especially important in times of drought or water rationing.
- Implementing greywater systems allows for abundant landscapes in locales where adequate water for irrigation is not readily available.
- Nutrients from kitchen wastewater, which would otherwise be wasted, are able to help replenish the fertility of soils.
- Greywater is easier to reclaim and treat than blackwater, and breaks down more quickly in the environment.
- Greywater systems can be implemented in new homes, and also retrofitted into older homes.
- Devices may be added to systems to capture and utilize heat from greywater, such as the hot water from showers.
- Some municipalities offer tax incentives for implementing greywater systems.
- Many municipal golf courses and public parks use treated greywater in their watering systems, which saves money for the community.
Disadvantages to Greywater
- Improper handling could impose serious health hazards.
- Some municipalities require expensive and complex permits and inspection to legally operate a greywater system.
- In some jurisdictions, indoor use of greywater may be prohibited.
- Implementing intricate filtration and treatment systems can be prohibitively expensive.
- Claims made by retailers of expensive greywater filtration systems may be inflated or incorrect.
- Greywater systems are poorly understood by many professionals compared with standard plumbing practices.
- Greywater systems require regular maintenance and may require replacement of expensive parts.
Inspecting greywater systems lies beyond the scope of a standard home inspection, according to InterNACHI's Standards of Practice, but here are some tips that inspectors can use in familiarizing themselves with them:
- Appropriate protective attire, such as gloves, should always be worn when handling greywater.
- Untreated greywater should not be stored longer than 24 hours.
- Irrigation should be implemented with drip hoses at the root level, or with sub-surface irrigation techniques. Greywater should not be applied to the surface of edible garden vegetables.
- Greywater should be applied intermittently in order to allow it to be properly absorbed by the soil.
- Greywater should not be used on exterior surfaces, such as patios or driveways.
- Only biodegradable detergents should be used for laundry.
- Pipes carrying greywater should be clearly labeled and should be kept separate from fresh-water and blackwater pipes.
- County guidelines should be followed when irrigating close to a drinking well.
- Systems should be set up such that excess greywater flows into the sewer system, and that sewage backup never causes greywater contamination.
- Only pipes with a diameter of 1½ to 2 inches should be used for greywater lines.
- In systems utilizing valves, only electric sewage valves should be used, as greywater may eventually corrode less expensive valves.
- U-shaped pipes should not be used for greywater, as particles may clog them.
- In order to determine the proper irrigation area, a percolation test should be used to determine the rate at which the soil will drain.
- Consult with local authorities to determine guidelines for greywater usage and necessary permit regulations.
In summary, greywater systems demand serious caution and proper handling to implement safely. But as water conservation becomes more important, especially in areas where resources are scarce, greywater systems are becoming an increasingly important option to augment traditional water supply systems.