Rainwater Harvesting

Ben Franklin said “when the well is dry, we learn the worth of water” (Richard’s Almanac, 173).

Source: Rodger Pickett

Rainwater harvesting is like our water management system in Utah.  Essentially precipitation comes mostly as snow, which is held as snowpack.  In the spring much of the runoff in many of our watersheds flows to mountain reservoirs where it is stored and later used in a controlled manner.  Rainwater harvesting follows this same pattern of storing water and using it later as needed.  While 2010-2011 winter snowpack is near an all time high the last one hundred year water history in Utah shows that drought conditions will repeatedly affect our climate and water supply every few years (see Palmer Drought Index Chart for Utah).

Do you know the average annual precipitation for your city?  This may help: Richmond 19.05”, Logan (USU) 17.70”, Brigham City 17.64”,  Ogden 17.12”, Bountiful 23.44”, Salt Lake City (downtown) 17.64”, Salt Lake City (zoo) 22.86”, Draper (point of mt.) 15.82”, and Spanish Fork 19.14.  On average a Utah landscape needs about 30” of  water a year, so you’re probably thinking you just need an extra 12-15 inches of rain, not true.  Much of the precipitation comes during the months plants need it the least ( late fall, winter and early spring).  As the Utah population continues to grow water will become even more scarce.

Rainwater harvesting has a long history dating back to ancient Native Americans.  Recent technologies and innovative methods have made it a viable solution in many situations.

In 2010 the Utah Legislation passed a new bill legally permitting the collection of rainwater on private properties (both owner occupied or leased).  The first step is to register with the Utah State Division of Water Rights.

Image Source: RainSaverUSA.com

The bill allows for two types of rainwater harvesting.  Above ground you may have (2) containers with the maximum size of 100 gallons each on-site.  The typical practice is placing a rain barrel at the base of a down spout.  Rain barrels typically come in sizes of 40 gallons to 100 + gallons and cost in the range of $80 to $200.  With rain barrels you want to make sure the water entering the container is filtered (to remove leaves and sediment), has a safe overflow option or path, and contains a tap at the base to easily attach a garden hose for distribution.

The second method is for underground storage and the law permits up to 2,500 gallons in one container.  The most common below ground containers may include fiberglass, polyethylene (plastic), galvanized metal, or constructed concrete vaults.  Fiberglass must be sited on a very smooth surface and is light weight.  Polyethylene is one of the commonly used and readily available.  Metal has a high risk rusting and losing waterproofing capabilities over time.  Constructed concrete vaults are commonly used, but as always concrete is susceptible to cracking and leaking.  The pros to concrete includes its ability to serve as a retaining wall, support above ground parking or walks, and can be designed into any size or shape.

Before purchasing a container it’s important to determine the appropriate size for your project.  There are two major

Image Source: Eco Home Magazine

factors when deciding on the right size they include 1) water supply and 2) planting needs or demand.  First to determine the supply you need times the area of runoff or impervious surface by the surface coefficient (asphalt, concrete, grass and etc) and then you look at the monthly rainfall intervals for your area.  Besides knowing how much water you can expect to receive on a given 1 inch storm you will want to look at the average monthly rain schedule for your area.  This will help you plan for and manage your water needs throughout the year.  The second important factor is understanding your landscape’s water requirements.  To do this you take the evapo-transpiration rate (ET) times the plant factor (drought tolerance) times the planting area times 0.623.  The evapo-transpiration rate is “an estimate of the water lost when a plant transpires or “sweats” through its leaves plus the water evaporated from the soil surface”.  These important steps help you know exactly your water needs for your area and specific plant types.

Once you have calculated the water supply potential and the landscape water needs, you will be able size the rainfall storage container.  It is important to understand that rarely is a storage container sufficient for irrigating your landscape throughout the growing season, most likely you will need to connect to a supplemental sprinkler system either potable or non-potable.  Most rainwater harvesting systems connect to irrigation systems anyway.

When developing a rainwater harvesting system to filter the rainwater correctly and sufficiently before entering your storage container.  Rainwater can be filtered mechanical through metal screens, biologically through bio-swales or wetland type plantings or through UV screening.  Once the water is collected, screened and stored in the container it is ready for distribution.  This is best done using a pump in the container or vault.  The water will be pumped from the container into your irrigation system.

Everyone knows that water is important, but often we forget that it is a fluctuating resource with a fixed potential.  In the future our water usage habitats for homes and landscapes will have to adapt to conservation in order to accommodate population growth.  Just like using mountains and reservoirs for storing water it is important we consider alternatives such as water harvesting and rain gardens.  Please feel free to contact Civil Solutions Group with any questions or needs you have.