Does Rainwater Harvesting Make “Cents” in Dry California?

February 25th, 2011  |  Published in Landscape Sustainability, Water Conservation

Each winter, California’s weather patterns shift.  Stagnant, high pressure systems that bring heat and dry are dislodged by powerful low pressure fronts.  This change brings cool weather and welcomed precipitation.

The window in which the precipitation falls is generally very short:  beginning in November and extending through March.  During this time, our native and ornamental landscapes soak up and use as much water is available to them.  The rest is rapidly evacuated through our urban and rural storm water management system, picking up impurities on its way to the nearby creek, river, lake, or ocean.

The rest of the year when natural rainfall isn’t enough to rain harvesting 001 Does Rainwater Harvesting Make Cents in Dry California?sustain our landscapes, we import water from points beyond while expending enormous amounts of resources doing so.  The cost of that water running out of our hoses and faucets is heavily subsidized by local and state agencies.  Seemingly unattached to the cost per gallon of water are all the direct and indirect costs that no one has yet been able to quantify.  How can one really put a price on environmental costs such as habitat degradation and salinization?

From a hypothetical viewpoint, harvesting and storing rainwater makes perfect sense.  Save what you get for free (rain) and use it when you need it (warm months).  But a common first question one asks about rainwater harvesting is “What is my return on investment?”  However, what they should really ask is “What are all of the benefits of harvesting rainwater?”.  

Rainwater Harvesting from a Financial Perspective

The reply to the first question, “What is my return on investment?”, is not an easy answer to give an inspired, eco-conscious crowd.  The bottom line is that the average homeowner will be hard-pressed to see a return on their initial investment (ROI) with a standard rainwater system.  Take a look at this example typical of a coastal, southern California climate to see why:

rainwater harvesting cost example Does Rainwater Harvesting Make Cents in Dry California?

This evaluation assumes the tank will be filled one time per wet season. Generally, the water collected in California's wet season is rarely needed until drier times. If your climate allows for multiple refills of the tank throughout the year, your ROI will be shorter. Filled twice, the ROI becomes 62.5 years. Filled three times, 41.5 years, filled four times, 31 years, etc. Also, depending on the price of water in your area, the ROI may increase or decrease.

If analyzed in strict dollars and cents without taking externalities into account, it makes no sense whatsoever.  But for the sake of argument, what happens if the price of water quadruples?  Well, then it starts making a bit more sense.  125 years for a ROI turns into a 31 year ROI.  And could the price of water ever sky rocket to those levels?  Don’t rule it out.  Consider when you purchase a gallon of water at the store:  that costs you over $1/gallon (a 25,000% increase over the cost of tapwater!).  That starts to put in all in perspective.  Regardless of the price, the issue of capturing and storing water goes far beyond the bottom dollar for stewards of the land.

“What are all the benefits of harvesting rainwater?”

The benefits of capturing and storing rainwater at your residence for later use are wide-ranging and have ripple effect through the landscape.  And the larger your storage system, the greater the benefits.  If you don’t have the space or budget for storage, there are many other ways you can utilize rainwater and improve conditions “downstream”.  For more on this, read about nine Simple Rain Storage Techniques.

Some of the benefits of capturing and storing rainwater:

It’s sustainable:  Using what falls out of the sky onto our rain harvesting 002 Does Rainwater Harvesting Make Cents in Dry California?homes and gardens is central to sustainable landscaping.  Why bring in something later in the season that you normally usher out of your garden with drains and pipes?

Provides clean water:  Throughout most of California, rainwater is wonderfully pure and has the perfect pH balance without any trace additives used to treat imported water.  Why not water your veggie garden with this?

Provides security:  Earthquakes, fires, and other disasters can cut your supply of water almost instantaneously.  If you have a couple thousand gallons, or even a 55 gallon drum with rainwater, you will have a bit more peace of mind.  A quick treatment of the water and you have some vital disaster security.

Provides protection:  If you live in areas where wildland fire is a real threat, having a backup supply for fire suppression is a no-brainer.

Improves off-site water quality:  In natural systems, rainwater slowly makes its way through a watershed.  During the voyage, it may rest in many locations allowing sediments and other pollutants to settle, thus cleaning the water.  But our development patterns hastily moves water from place to place, rarely allowing it time to be cleaned or filtered.  By storing water on site, you are reducing contaminated run-off, and in turn, increasing water quality.

Reduces erosion:  Behind clean water, soil is our most valuable resource.  Without healthy topsoil, our landscapes, farms, and open spaces become barren.  In addition to chemical fertilizers and development practices, run-off is another cause of our dwindling supply of quality topsoil.  The more run-off there is, the more soil erodes.

Reduces demand on existing infrastructure:  An enormous cost of the water you use  goes towards maintenance of the infrastructure serving your water district.  Pipes, canals, treatment stations, pumping stations and other components of a water system are under continual wear and tear because they are working beyond designed capacities or intended life span.  By reducing the demand on the infrastructure, we reduce the cost of water for everyone.

Although rainwater harvesting may not make strict financial sense, the above illustrates there are many reasons to choose to do so.  As a society, we spend money on countless frivolities that provide far less return than a rainwater harvesting system.  Of course most purchases have a direct and immediate impact on us.  Yet spending money  now to benefit the whole is much less expensive than waiting until changing conditions force us to do so at a far greater expense.

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