At the beginning of the month, Shiran Ben Hamu and Eden Assulin, two twelfth grade students who live near the border with the Gaza Strip, were awarded a prize by Tel Aviv University after proving it possible to water gardens with water that had been used for laundry and to wash floors. But the issue of so-called gray water shows clearly why acting green isn't always as simple as it may seem.

A rainbow of classification

The question is what qualifies as gray water? Ben Hamu and Assulin used laundry water, but there are others who caution against doing so. Laundry water is controversial because of the high concentration of detergents and cloth fibers, which render it not recommended for irrigation.

The meticulous regard it with the same caution as sink water, which can possibly contain problematic residual organic substances and is considered to be black-gray water (a step up from toilet water, considered completely black). The best gray water comes from a shower or cleaning floors, since there is only a minute concentration of problematic substances in the water.

According to that same principle, water used for meat and dairy products (including fish) is differentiated from water used for cooking other foods. Water used for cooking, soaking or washing vegetables, fruit, lentils and grains is also good for irrigation.

The designated sink

Illustrating the lengths some must go to for gray water recapture is an appliance known as the designated sink. It is designed to treat water that has come into contact with meat and dairy products, which would normally be cost-prohibitive to recycle. Even among die-hard environmentalists, there are many who believe that a sink of this kind shows how the tail wags the dog.

After all, before selling and buying all kinds of appliances that make life more complicated and expensive, it is possible to take a few simple steps. For example, one could instead keep closer tabs on water usage and start collecting rain water and water from air conditioners.

Cleaning materials

There is no argument over the fact that the stronger the cleaning agent, the less one is advised to use the water in which they are found for irrigation. That is why grease removers of all kinds are forbidden. The same holds for bleach. There is of course an argument over where to draw the line. Whoever wants to err on the side of safety should move over to ecological cleaning materials altogether.

What can be watered?

Some people recommend that one avoid irrigating even grass and vegetables with gray water. They are much more sensitive to harmful materials in the water. On the other hand, ornamental trees are less sensitive. Fruit trees are a matter of controversy and experts recommend irrigating them with a drip system through the soil and not by sprinkling from above.


The central problem when using gray water is logistic, since these are not standard arrangements. A relatively simple solution is to channel all the gray water into a tank in the bathroom using a container and a pump. There are more complex systems and even more expensive ones that are offered by companies specializing in recycling gray water. (An Internet search will reveal a list of agronomic experts that install these kinds of home appliances.)


Workshops are held all over the country to gather practical instructions about how to set up systems for purifying and filtering gray water with home appliances and at a reasonable cost. The idea is to recapture water that is clean and environmental. Topics can include taking water out of the house, preliminary filtering, separating out oils, putting the pipes and containers for collecting the water in place, and irrigating.

Additional reservations

The most cautious of the cautious claim that even cleaning materials that are deemed ecological are not entirely problem free. It is true that they contain less phosphorous but they still have a lot of salts which should not be returned to the water cycle, at least in the long run.

In short, be careful. On the other hand, others claim that there is a limit to fears and threats. After all, people also spit in their gardens, or worse.

Those in favor of using gray water fear that behind all the warnings lie merely the interests of companies that want to sell us appliances for filtering and purifying vegetables.

Those who are flexible on the issue of gray water say that there are only a few rules that one must be sure to follow - the ban against using water from sinks and toilets, filtering the water especially of fibers from cloth, and making sure that there is a constant flow, since standing water can harbor bacteria. They are also lenient when it comes to the use of cleaning materials and recommend merely that the quantity be limited.