Justifying Rainwater Collection: Calculating the True Cost of Cheap Water

The other day I got a question that I get all the time.  It is a good time to answer this question in a public forum, especially considering the rainy season is almost upon us.  We can all benefit from changing the way we think about our water resources.

Q:  In running the numbers for rain barrels, filling a 1500 gal barrel twice equals 3000 gal or 4 HCF. That's just under \$15 (this is at tier 1 costs). which makes the payback for a \$1500. system equal to 100 years.

These numbers are hiding a lot of costs that we are not thinking of as we turn on our tap and let the water flow out at pennies per gallon.  What if we start to factor in some of these hidden costs?  What would our cost/benefit analysis look like?

This 1500 gallon tank was put in the front yard of a Rancho Bernardo home and painted white.  This in conjunction with a greywater system from the garage and a low water use landscape helps this family keep their front yard beautiful and abundant.

First of all let's readjust our expectations of the costs involved in setting up a 1500 gallon tank.  You can get a 1500 gallon rainwater tank from  The Tank Source, located in Alpine for about \$900.  This tank has about an 8' diameter, which is certainly doable for some but not all residents.  A 1000 gallon tank with a 6' diameter is a little more realistic for most urban homes here in SD, at a cost of about \$750.  You can see that it is more cost effective to get the largest tank you can.  If you want to set the 1500 gallon tank up yourself, you would need a couple filters at a cost of about \$80.  You will need some pipes and parts, totaling between \$250-\$400 depending on the distance you are taking the water from your house and a few other nuts and bolts.  This can look like as little as \$1000!  Or if you have a professional install this tank, you may expect to pay about \$350-\$500 in labor costs.  Now we are getting up to \$1350-\$1500.  But did you know that the City of San Diego is offering up to \$400 in rebates for rainwater tanks?  The County of San Diego is also offering \$75 per barrel.

Some of you may be wondering if it is even possible to get 1500 gallons of water off your roof in our arid climate.  The answer is ABSOLUTELY!  Check out this amazing rule of thumb and compare it to your situation:

A 1000 square foot roof will yield 600 gallons of water in only 1" of rain

It rains about 10" here in San Diego.  So you can fill this tank up in less than a third of our rainy season, which means you may be able to fill it up THREE times even, if you can find something to use the water on in between rains.

Those are the basic nuts and bolts of this example system, but let's delve further into the cost of water. Consider that water in Southern California is excessively underpriced for its actual cost with regards to energy, environmental, and legal impact.  You can decide for yourself whether or not you think this is a true statement after we consider some additional information.  You could start by reading  Cadillac Desert, by Marc Reisner to help you understand the intricacies of how and why our water infrastructure was built.  As we become confronted with the reality of the related costs associated with cheap water, prices will raise significantly, and any conservation tactics we have put in place before that time will greatly reduce our dollar cost in the future.

Did you know only 20% of our water comes from local sources?  The remaining 80% comes from both the Delta region up in the Bay Area and the Colorado River.  This means a few things.  First of all a drought that may be affecting other regions, and not us directly will certainly impact our water supply.  Also, there are legal battles ensuing over Colorado River water and Delta region water than may reduce the amount of water coming to Southern California.  Let's imagine you have a valuable investment like an established fruit tree, or many.  If there are drought restrictions in place that limit how much you can water your garden (kind of like last summer), wouldn't that water in your 1500 gallon tank become more valuable to you as asset protection?

Did you know that 20% of California's energy costs are associated with moving water around the state, including the incredible feat of pumping our water supply from the State Water Project 1,926 ft over the Tehachapi Pass north of LA.  So let's add some energy costs into the cost of getting our water out of the tap.  Let's also factor in the benefit of having an emergency water supply on hand if power is disrupted for any reason for any length of time.  Maybe that water supply is for protecting your established food production, or maybe it is even more valuable as a drinking supply.  Can you calculate what bottled water will cost per gallon in an emergency and compare that to the cost per gallon of the water you have stored in your tank?

This 1320 gallon Bushman tank overflows onto the hillside which was reworked to hold rainwater flowing on it into basins around the fruit trees.

We have only been addressing water supply issues, but what about the value of mitigating storm drain runoff?  How many of your tax dollars are allocated toward dealing with storm drain pollution, or even urban flooding associated with the massive volume of runoff created by paving over as much as 80% of our permeable surfaces in urban areas?  If all of us put at least some of our rainwater from our roof into rainwater tanks, and then redirected the remainder of our runoff into our gardens, which were landscaped to hold water using basins, mulch, and appropriate plantings imagine how much money could be saved at many levels.  Think of tax dollars and grant funding being used to clean up waterways that get inundated with polluted storm water.  Think of tax dollars being used to repair and clean storm drains every season!  Think of redirecting this money to funding education in schools and communities and rebates for systems that serve the double purpose of augmenting a limited local water supply!

Now if you are going to use this very expensive water source to keep your lawn green, you might not consider a rainwater tank cost effective, especially if we look at some very simple figures.  Lawns typically require about 50" of water to stay green throughout the year.  It rains about 10" here in SD.  If you run the calculations of applying 40" of water to 500 square feet of lawn, you realize 13,000 gallons of precious water are required to keep that lawn green.  It is hardly worth storing 1500 gallons, or even 3000 gallons to maintain this aesthetic.  Why not get rid of the lawn and plant something that can be maintained with that 3000 gallons, like natives, or Mediterranean plants such as the Nifty 50.  Native plants maintain a diminishing local ecology which is being threatened by paving and invasive plants.

This 1320 Gallon Bushman Tank overflows into the 205 gallon Bushman tank.  These tanks are harvesting off 450 square feet of roof and fill up twice in an average year of rain.  The water is used all winter on veggies, chickens, and trees to make room for the next inflow of rain.

There is great value to using our precious water resources to grow food locally.  There is an even greater water footprint than what we see on our water bill every month, associated with goods and services we buy and support.   Try to imagine that an orange brought in from Florida has a higher fossil fuel cost, which has an associated water cost, than something grown here in California.  Furthermore, an orange grown in an industrial agriculture setting will have a higher associated water cost than one grown in your backyard.  Furthermore an orange grown on rainwater in your backyard will have the lowest water footprint of all!

This is a lot to take in when you are justifying the purchase of a rainwater tank.  Food for thought: why not consider using greywater!  A simple Laundry-to-Landscape system which sends your laundry water (non-toxic, organic, sodium-free soap included) to your trees and shrubs can cost as little as \$150 in parts, or \$500 installed by a professional.  If you run 4 loads a week on an older front load washer at a rate of 35 gallons per load, you'll be making over 7000 gallons of water available to your landscape over the course of a year.  If you combine this with trees and shrubs that are actually producing food for you that you don't have to buy from the store, and you take into account the additional nutrient content of this water as a fertilizer that you don't have to purchase and will increase production of your plants, you can see some pretty astounding justification for this water conservation strategy!

Contact Brook Sarson with H2OME at brook@h2o-me.com to schedule a consultation!