The reality is that watering every day, with a little water, provides a much better outcome (both in saving water and providing better growth) than watering heavily twice or less per week.
Capillary effects are the key. Before reviewing different methods of using graywater, we will spend a few pages on what Capillary Irrigation is, and why it is the most important concept of all.
The water droplets at the edge have fewer neighboring water droplets, so they cling more tightly to those around them; this is known as surface tension. Now gently dip the corner of a paper towel in the pool of water. The water is attracted to the paper and “climbs” up the paper towel – this is capillary action.
If the soil is dry, the surface tension of the edge of the water pool prevents the water from spreading outwards quickly.
The effect of gravity pulls the water down, into the root zone, and if there is more water than the roots can take straight away, it keeps going down, into the subsoil and much of it wasted,
To summarize, for soil, water moves slowly through dry soil, and relatively quickly through wet/moist soil.
How does Capillary Action help graywater irrigation?
Note that if the garden soil is very dry, surface runoff may occur. This is common in drought areas, where the soil is so dry it has become hydrophobic (i.e. repels water).
Soaps and surfactants in the graywater help to breakdown the water resistance, and surface runoff in most cases ceases within a day.
In this example, three dripperlines are needed in the garden bed.
When planning and installing a graywater irrigation system, remember to “water the garden bed, not the plant”.
Because less dripperlines are required, planning and installation are much easier.
Dripperlines do not need to be near the plant and can be as far as 3′ away (in loam/clay soil).
Even without any irrigation or rain over the hot summer months, my green strip stays green, while neighboring strips go brown.
Graywater is being sucked under the sidewalk, uphill into the green strip, all because of capillary action!