The vast majority of plants thrive on graywater, and the nutrients contained within. They do not need potable water, and perform better with graywater.
This chapter outlines how graywater affects plants, and precautions that should be taken to ensure your garden becomes an oasis relying solely on graywater.
- Do NOT store graywater for more than 24 hours.
- Only use laundry detergents that are very low in sodium (salt).
- Distribute graywater evenly across the garden – don’t kill plants with kindness by over watering.
- Take care with graywater distribution if using movable hoses connected to the washing machine outlet.
- Avoid any cleaners containing Boron – this is toxic for plants.
Remember that what goes down the drain is going onto your garden!
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 lawn.
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 negligible due to dilution.
Typical bar soap has a pH of around 7. Again this is highly diluted within the shower/bath and has little impact on the garden if well dispersed.
Washing Machine Water
Washing machines are a popular source of graywater, simply because the inbuilt pump makes it easy to divert the water from the sink to either a surge container with dripperline connected, or directly out to the garden via pipes/hoses.
Non-concentrated soap powders typically contain high levels of sodium (salt), used as fillers. Use only 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 wash 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 washing 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.
I 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 balanced by the following rinse cycles (the overall pH level of washing 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.