Below Ground Water Storage — Water Wicks Can Be An Option
When we hear the term below-ground water storage, a buried cistern is what usually comes to mind. Yet there is another approach that has been used for centuries — a water wick. These structures hold water and release it slowly over time. They are also commonly known as Watson wicks or pumice wicks.
It has been known for centuries that mixing organic materials into soil helps it absorb and retain water. Water wicks are taking this concept to the next level by providing a large, constructed basin for this water storage.
Water wicks are typically constructed with pumice, a form of volcanic rock that floats and absorbs water due to its highly porous nature. Where pumice is not readily available, scoria is often substituted. Both come in a variety of colors and sizes and both absorb water and slowly release it.
The general concept is to bury the water wick under the planting area. The roots grow into the wick and pull up the water when needed. The wick holds water longer than regular soil, thereby providing plants access to a “passive” water container. Water wicks are typically constructed about 24 inches below ground, beginning with about 12 inches of pumice, covered with about 6 inches of sandy soil, covered with about 6 inches of planting soil, and a few inches of mulch on the top.
The size of the wick area varies depending on what is draining into the pumice wick, how big a planting area you are creating and what you are planning to grow.There are also variations on what is installed under and around the wick and whether the wick is equipped with an overflow so that the plants do not become saturated in the case of too much water being fed into the bed.
Water wick systems can be made to receive water manually or from alternative water sources such as rainwater, greywater or blackwater. With greywater and blackwater, the water needs to be specifically pre-treated prior to feeding a wick. Many greywater systems installed today incorporate a wick-type system and while blackwater systems don’t, they could.
These alternative sources of water may need permitting in some locales. It is always a good rule to check with your local or state permitting agency to find out what is allowed.The concept that some materials are more absorbent than others is an easy concept to grasp. Just submerge a sponge or a paper towel in water and watch it soak up water.
Over time both of these materials will dry out due to evaporation. Under ground, pumice or scoria act the same as a sponge, soaking up water and storing it in the multitude of air spaces both contain. Since they are buried they will typically not lose this water to evaporation, but will release this water to the surrounding area.
Water wicks are not the solution for every watering need, but they can be a solution for many gardeners. When integrated with a rainwater, greywater or blackwater system, they provide a great method to reuse water onsite and reduce our water footprint. In Northern New Mexico, there are many professional firms trained and capable of installing a pumice wick system for you.
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