City-Data Forum Rain Harvesting (Phoenix, Tucson: HOA, credit, big house)
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05-30-2011, 07:42 PM
 57 posts, read 157,752 times Reputation: 61

I'm interested in doing this. Has anyone had gutters and the appropriate storage combo installed at their house?

Based upon the average rainfall and the sqft of my roof it looks like I would be able to potentially harvest 12000+ gallons a year. That seems like it would be a huge saving in water that I could use for a variety of things.

05-30-2011, 07:57 PM
 240 posts, read 723,717 times Reputation: 395
Not at our house, but at one of the recreation centers here in Dobson Ranch. We have a nice rose garden in our community, and the collected water is said to "provide at least 50 percent of the water the roses need on an annual basis." The tank is underground and covered on top with permeable pavers. Pretty neat. Anyway, if you want to read more about it, here is a page that talks about it.

05-30-2011, 10:26 PM
 17,643 posts, read 36,124,679 times Reputation: 10159
12000 gallons from rainwater, here in the Valley? Where do you get THAT number?

05-30-2011, 10:47 PM
 Location: Green Valley, AZ 351 posts, read 795,344 times Reputation: 311
It's simple if you know how to crunch the numbers. Assuming you have a 2400 sq foot home, and knowing that Phoenix get's an average of ~8 inches of rain per year, you just crunch the numbers:

8 inches of precipitation = 2/3 feet.
2400 sq ft roof * 2/3 foot precipitation per year = 1600 cubic feet of water per year.
1 cubic foot = ~7.5 gallons, so:
1600 cubic feet * 7.5 gallons/cubic foot = ~12,000 gallons.

For this specific example you can expect to loose maybe 20% due to evaporation, so in reality you would get closer to 10,000 gallons of usable water (assuming your storage tank is that big). A bigger roof = more captured rain, but you must have a tank large enough to catch it all, otherwise it's a waste of gutters.

To put that amount of water in perspective, it's about the same as a 12x24 foot swimming pool that is 4.5 feet deep.

05-30-2011, 11:49 PM
 17,643 posts, read 36,124,679 times Reputation: 10159
The problem with the rain here is that it is so spotty, especially in the monsoon months, you may live in a part of town that sees nothing for months on end, and doesn't see 7-8 inches in a year. How fast that rain falls also affects evaporation rates, too. One gullywasher will have less evaporation than several small showers, but they all count the same in those "inch" statistics. http://voices.washingtonpost.com/cap...t_does_it.html

Have at it if you think it's worth it, I've lived here all my life, and would never think of bothering to put such a system in. Gutters all around to keep clean? There's enough to do with the gutters I have. Frankly, the water usage part of my utility bill is just not that big, and it isn't as if you can use this water for everything.

The Dobson ranch rose garden system only provides half of what those roses need in a year? It sounds nice that they can say they are "saving" water, but that's not where I'd want my HOA dues going.

Last edited by observer53; 05-30-2011 at 11:57 PM..

05-31-2011, 07:46 AM
 57 posts, read 157,752 times Reputation: 61
..

Well personally I think it is worth it if done correctly. It is a desert climate and there is no reason not to take advantage of what little water there is.

I think I read something where the Tucson city council has said that all new commercial contruction will source atleast 50% of its water via rain harvesting. This is starting to find a huge push across arid climates in US.

I've also got solar panels and the like. I try and roll with the lowest impact highest return for the area.

06-01-2011, 02:55 AM
 Location: Green Valley, AZ 351 posts, read 795,344 times Reputation: 311
Quote:
 Originally Posted by observer53 The problem with the rain here is that it is so spotty, especially in the monsoon months, you may live in a part of town that sees nothing for months on end, and doesn't see 7-8 inches in a year. How fast that rain falls also affects evaporation rates, too. One gullywasher will have less evaporation than several small showers, but they all count the same in those "inch" statistics.
True, but with that variation you can also expect to get more than the average some years, and less than average others. One year you may get 2 inches of useful rain, and 14 inches the next. Maybe all you need is that one "gullywasher" to fill up the tank, and maybe if you planted low water plants and trees, a full tank could last you a whole year. The water hungry Dobson Ranch Rose bushes will require 1 to 2 inches of water per *week*. It's hardly the ideal choice for the Phoenix area. They should have considered this when they designed the garden. If the right plants and trees are planted, potentially no additional water would be needed.

Rain harvesting is ultimately a personal decision. It definitely will become more valuable and viable as the water supply dries up and demand continues to increase far past sustainable levels. If a water shortage were to occur in Phoenix in the next 20 years, without an alternative source you will just have to let your plants die. Why not be proactive about it and help to solve the problem instead of exacerbate it, all while maintaining a beautiful semi-arid garden.

06-01-2011, 03:02 AM
 17,643 posts, read 36,124,679 times Reputation: 10159
Quote:
 Originally Posted by vjsoto True, but with that variation you can also expect to get more than the average some years, and less than average others. One year you may get 2 inches of useful rain, and 14 inches the next. Maybe all you need is that one "gullywasher" to fill up the tank, and maybe if you planted low water plants and trees, a full tank could last you a whole year. The water hungry Dobson Ranch Rose bushes will require 1 to 2 inches of water per *week*. It's hardly the ideal choice for the Phoenix area. They should have considered this when they designed the garden. If the right plants and trees are planted, potentially no additional water would be needed. Rain harvesting is ultimately a personal decision. It definitely will become more valuable and viable as the water supply dries up and demand continues to increase far past sustainable levels. If a water shortage were to occur in Phoenix in the next 20 years, without an alternative source you will just have to let your plants die. Why not be proactive about it and help to solve the problem instead of exacerbate it, all while maintaining a beautiful semi-arid garden.
14 inches? Well, let's not exaggerate too much. A lot depends on the cost of the system. The problem is, we say water is precious, and should be conserved, but the price that is currently charged for it doesn't really provide any incentive to do that. Unlike other improvements, there are no tax credits that I'm aware of, and how long would it take to recoup the cost, figuring in only the cost of the water that I use outside?

For me, what might happen 10-20 years down the road, when I'm likely no longer in that house and am using even LESS water, doesn't make this anywhere near the top five of my household priority list.

06-01-2011, 03:47 AM
 Location: Green Valley, AZ 351 posts, read 795,344 times Reputation: 311
Quote:
 Originally Posted by observer53 14 inches? Well, let's not exaggerate too much. A lot depends on the cost of the system. The problem is, we say water is precious, and should be conserved, but the price that is currently charged for it doesn't really provide any incentive to do that. Unlike other improvements, there are no tax credits that I'm aware of, and how long would it take to recoup the cost, figuring in only the cost of the water that I use outside? For me, what might happen 10-20 years down the road, when I'm likely no longer in that house and am using even LESS water, doesn't make this anywhere near the top five of my household priority list.
Well, 2" is just as exaggerated, but I didn't see you roll your eyes at that number.

Again, it's a personal decision. I'm buying some land in the Tucson area and will eventually build a house on it. Tucson is blessed with 4 more inches per year than Phoenix gets, so rain water harvesting is a bit more practical here. I plan on harvesting a little bit into an underground tank and also use grey water (washing machine and bathtub water) for irrigation. The goal would be to become completely independent of tap water for plant irrigation while maintaining a nice green shade filled yard. It's very low maintenance and I'll never have to worry about letting my plants die if there is a water shortage. Yea, the initial investment may be a little high, but I'm thinking long term (30+ years down the road).

06-01-2011, 11:58 AM
 Location: Peoria, AZ 162 posts, read 368,798 times Reputation: 151
I'm thinking of doing this, but I've done my own calculations and I don't seem to remember comming up with that big of a number. 12k gallons/year is a lot and I think it's a pipe dream. My plans are to store the water in a pond that I have in front of the house. It can hold probably around 1500 gal. I have a pretty big house, but since it is a two story house, its footprint is smaller than yours, I estimated its area to about 1850 sqft. and calculated that it should be able to give me about 7000 gal. I really wish I had a bigger piece of land away from the city. It would be awesome if I could get a big underground storage tank (5000 gal or more, and set up a sloped area on the property as a rain harvesting area (on top of the roof area) ... or I could just move back to seattle and never worry about rain again.
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