Green energy applications: Gray water – white use

What is gray water?

‘Gray water’ is water that is used at home in places such as a bath, floors rinse, sink,  dishwasher water and similar. All of these except for flashing the toilets and gardens watering. These waters are, in fact, about half of total domestic consumption. Member of Kneset, Astrina Tartman recently engaged in promoting a law for gray water use. “The use of gray water may bring savings of about 50% of water consumption in households” explain initiators of the law. As to the prosed law, every new house built will be obliged to install piping system suitable for recycling of “gray water”.

Legislation in the world

In 2002 a law passed in Arizona encourages the use of gray water. Essentially it is a liberal law and determines number of rules of “to do” and “not to do”. In many countries such as USA, Australia, Germany and Japan many use gray water for flushing toilets and watering gardens, for many years. State of Israel knows how to use the gray water more efficient that most countries in the world and in fact makes use of over 70 percent. Today, many wastewater purified up to “secondary” level, i.e., water that can be used in agriculture that is not for food (like cotton). Few treatment centers bring the water to “third” level which is similar in quality to drinking water. ‘Shafdan’ currently succeeds, with gravitational filtration (transfer of water through layers of sand) to bring the water to a level comparable to drinking water quality. In addition, today Shafdan manages  approximately 25% of the total recoverable amount of water, on the other hand, the infrastructure of gray water almost does not exist.

In American law the definition of a private home water consumption: a structure that produces up to 400 gallons of gray water a day (about 1.6 cubic meters). In future the structure that will not only produces the gray water, but will also consume them without transferring them to other. The American law also applies few restrictions on this water: prohibition of irrigation sprinklers, watering of herbs and vegetables, limiting the maximum size of the storage tank of 55 gallons (200 liters), emptying the system every 24 hours (after which the water is considered as black water), closed and secured container and security for children.

Since the establishment of the law it was adopted by 12 states and a similar number of states are considering it these days. In addition, with minor changes,  the law was adopted by Australia, Japan, Germany, England, Jordan and Cyprus. Cyprus and parts of Australia also instituted an economic system to subsidize private economies who install gray water return system. In Israel, belatedly as usual, there are parallel activities of several members of the Knesset to pass the legislation, in conjunction with U.S. law.

Laundry water mixed with detergents

Laundry detergents get a lotr of criticism, not always justified, although some of the urban legends about the damage in laundry water, somewhat true. Laundry detergents contain 4 problematic minerals:

First, salts: a harmful to soil substance found in washing powder in big quantities. The survey conducted by the Ministry of Environment, reviewed three types of washing materials: washing liquid, washing powder compact type (small bags) and ordinary washing powders. Survey found that the washing fluids, do not consist salts at all, and in  washing powders there is a reasonable amount of salt. The ministry checked and found (in cooperation with Shenkar College) that the amount of laundry detergent can be reduced by half of the recommendations of the manufacturer and get the same result in terms of cleanness of the laundry. Unfortunately, despite the obvious conclusion, apparently fearing from the power of the manufacturers of laundry detergents, no campaign to switch to powders such as compact or liquid detergent or reducing the use of quantities in washing powder was launched.

Boron is a material which generally causes long-term sealing of ground. Because of the high boron concentration in the treated sewage water, which causes considerable damage to agriculture, and a desire to increase the level of use of recycled water, the State of Israel established in 2004, more courageous and surprising law, also compared to the rest of the world. The law determined that the washing powder boron level will decrease each year by up to 0.5 grams per kilogram product. Year of 2008 was determined as final year to reach the target. A survey conducted by the Environmental Protection Agency back in 2006 found that companies already complied with the reduction of boron level to reasonable and harmless level.

Phosphorus and potassium: these materials are used for cleaning laundry but after disintegration create excellent fertilizer for the garden. There is a research for this matter as well.

The conclusion of this review was done by Moti Nir, specialist for gray water systems, is that levels of harmful minerals in the washing water are very low today and comply to standards without any fear. Urban planning can yield gray water projects in new neighborhoods, public buildings and hotels. Integrating gray water recycling systems in green building will strengthen the environmental positioning and enormous economic savings.

Construction until now – problem

According to the proposed law, as stated, every new house built in Israel will be obliged to  install piping system suitable for recycling gray water, ie dual piping system that is necessary to distinguish it from other water supply.  But what about rest of the households,  hundreds of thousands existing and those which are in construction prior to approval of the law and its implementation? Adjustment of existing residential buildings pipes, is not feasible and therefore the approval of the law for use of gray water as soon as possible is very important, considering the poor situation of the water situation in Israel.

And what about the agriculture?

One argument that is used is that if there was a shortage of water, then the price to farmers shall be increased. In practice, farmers prefer recycled water because it’s cheaper than fresh water. The problem is that recycled water can not be used to irrigate crops for food. For this reason and others the farmers continue to use fresh water. Another reason for which farmers use fresh water is its cost of transportation. Treatment centers are located near population centers, and agriculture areas s.a. Galilee is distant from them. Using existing infrastructure it is easier to transfer clean water over distance. It is clear today that the key issues with the gray water solution are health and safety problem. Ministry of Health still is not able to make courageous decision to approve the use of ray water or completely prohibit it entirely (a decision that of course will be completely wrong since it has been experienced in many parts of the world quite successfully).

More on this topic can be found:


Gray water recycling system is a system that receives water from showers and sinks that are not in the kitchen or in the toilets (some systems also use water from dishwashers and washing machines) and returns it for use in flashing the toilets and watering the gardens, if thare are no fruits and vegetables in the garden. It is important to understand that gray water recycling adds value in several areas: reducing water losses of municipal pipelines, saving municipal sewer infrastructure investment, saving the marginal costs of desalinated water production, security in water supply for gardening during water crisis times, all of those with savings for the consumer. Currently, water restoration technology is of the shelf technology and as the sooner we will implement it into practice is better. Proper fit of implementation projects will ensure proper treatment required for recycling, without public exposure and health risks while saving resources.