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Capillary Action Effects

Traditional garden irrigation systems are designed to provide a wet and dry soil moisture cycle.

An example of this is watering every second day, with enough water to stop the soil becoming too dry before the next watering cycle activates. The soil is continually moving between wet and dry cycles.

Graywater, however, should be irrigated immediately (especially when taken from showers),  to prevent odor development.

Most people are surprised to find out that daily irrigation makes designing and installing an irrigation system much easier.

Capillary Action

Capillary action is the process of water moving from a wet area to an adjacent dry area through a porous media. It can be a slow process, especially in soil.

A good example of capillary action is placing a blotting sheet over a water spill. The water will soak into the immediate area of the blotter, then slowly spread further out from the spill. If you add some more water to the top of the blotter, at the center of the first spill, the water spreads around the damp area of the blotter quickly - while the edges of the blotter stain still expand relatively slowly.

To summarize, for soil, water moves slowly through dry soil, and relatively quickly through wet / moist soil.

How does Capillary Action help graywater irrigation?

Because graywater can be irrigated in the garden every day, the soil builds up moisture levels a significant distance from the immediate irrigation point. Water spreads quickly away from the irrigation point, avoiding issues with surface runoff.

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.


Wet / dry irrigation requires more
concentrated dripperlines to enable
water to soak into the soil without

In this example three dripperlines
are needed in the garden bed.




Moist soil requires only one
irrigation dripperline for the same
size 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 is much easier.

The key concept is "water the garden bed, not the plants".

Dripperlines do not need to be near the plant, and can be as far as 3' away (in loam / clay soil).

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