1) You locate a downspout on your property that drains near an area that is good for growing plants and has room for the footprint of a 55-gallon rain barrel (likely a used olive oil barrel). For the sake of simplicity, let's say this downspout drains 500 square feet of roof area. Using the design provided by www.rainharvester.blogspot.com you stack two rain barrels giving yourself 110 gallons of capacity. According to the website, the apparatus can be constructed for five cents/gallon, or $5.50, plus time (that nonrenewable resource), assuming you can get your barrels for free. This sounds optimistic to me, so lets say the cost of the barrels is $20 each (current price off craigslist), and the cost of additional parts and tools is $10, for a total of $50.

2) Here in Chico I tend to need to start irrigating as early as April and I don't stop until sometime in October. Average monthly rainfall during this time is 2" in April, 1" in May, 0.5" in June, negligible in July and August, 0.7" in September, and 2.6" in October. So here is the math--Your two barrels start off full in early April. You drain them during a dry two weeks, it rains, they fill, and you drain them again (220 gallons used). It rains once in May and once in June enough to fill the barrels with water you use to nurture your tomatoes (220 gallons used). The next significant rainfall isn't until mid September, which fills your rain barrels with enough water to help two young fruit trees (110 gallons). Your barrels fill and drain twice more in October (220 gallons used), and despite a mid November rainfall, an unseasonably warm dry spell at the end of the month leads you to draining the barrels one more time (110 gallons used) before the winter wet takes hold.

3) So for one season, you've used 880 gallons of captured rainwater to irrigate during dry spells. Pretty good, until you consider that Chico's water rates are less than a dollar per 748 gallons (1 CCF). In short, you will save water by purchasing and installing a couple rain barrels, but you won't save any money, at least not until water rates increase dramatically or until we see a rain barrel rebate program like what they have in Palo Alto ($50).

But I'm not quite done. Let's look at my house, and economies of scale. I've identified a pair of downspouts that flank the rear of the garage that collectively drain 980 square feet of roof from the garage and part of the house, yielding 610 gallons of water for every inch of rainfall. A row of 12 stacked rain barrels along the back of the garage could give me 660 gallons of storage, thus allowing me to hold at least an inch of rainfall at a time.

Using the same math as before, I might be able to harvest and use 5280 gallons of water a year, or just over 7 CCF. Note that would take the place of treated groundwater that I am presently purchasing from the California Water Service Company. Economically speaking, if I can install the system for say, $70, then I break even after 10 years (assuming water rates average $1 during that time).

My takeaway: As one might expect, the best way to save water and money is simply to use less water. The best place to start is making alterations to irrigation/landscaping, which is the biggest water hog for many Chico residents.

As far as rain barrels are concerned, I think a minimum of 5000 gallons of capacity should be standard on all new construction of all structures that have any amount of landscaping. As far as creating a new system for an existing home, you've read the blog, you're likely aware of the value of water (whether or not this is reflected by its present dollar value); I leave it up to the reader to make their own choice.

My wife and I plan on going for it. Anyone have twelve 55 gallon barrels they would like to unload?