Gardens do not need clean, potable water to flourish. The vast majority of plants thrive on graywater, and the nutrients contained within.
This section of the website outlines how graywater effects plants, and precautions that should be taken to ensure your garden becomes an oasis relying solely on graywater.
Shower water contains soap, shampoo and conditioners. The amount of fats, sodium and phosphates in shower graywater is negligible, and has virtually zero impact on plants and turf.
A common misconception is that all graywater is alkaline, and that acid loving plants do not grow as well with graywater. Azaleas are often quoted as a plant that does not enjoy graywater.
Many graywater gardens include Azaleas, and have experienced as good growth, if not better than irrigating with potable water.
The PH of shower water is largely dependent on the type of shampoo used. While most shampoos are near neutral PH, some fruit based shampoos can be slightly acidic. Again the effect on PH overall is neglible due to dilution.
Washer Machine Water
Non concentrated soap powders typically contain high levels of sodium (salt), used as fillers. Only use concentrated powders that claim to be low in salt, or use liquid detergents.
Almost all detergents will produce highly alkaline graywater (PH approximately 10.5) when releasing the first wash water. Repeated application of concentrated highly alkaline water to one or two areas of the garden will kill plants.
This is of particular concern when DIY connecting a 1" hose or similar to the washer outlet, and leading the hose to a garden area.
A common problem in Australia is the use of a manual gravity fed hose connected to the washer machine - people would move the hose from one area of the garden to another between wash cycles. Being creatures of habit, many people always moved the hose the same way each wash. As a result the first (dirty and high PH water) ended up in the same area each time, raising the soil PH level and killing plants in the area.
We fear this will occur in California due to their unusual requirements for a 'simple' system in the recent CA code update, which appear to encourage this style of irrigation.
However, if graywater is irrigated evenly across the garden, the high PH water will not concentrate in one area, and is in fact partially balance by the following rinse cycles (the overall PH level of washer machine water (including rinse cycles) is typically in the range of 8.0 - 9.0).
Water softening agents use large amounts of salt. Softened water should not be used in the garden.
Further Information about graywater:
Fruit & Vegetables