Water Usage – How much do we need?

One of the areas on my list of major short term projects is to get rain catchment setup, or at least modeled.  The first question that arises is “How much water do we use in a day?

This question alone is an interesting one, and at least here there is some research we can draw from.  For one, there are sites like the American Water Works Association (http://drinktap.org) who list the following per capita uses:

Use Gallons per Capita Percentage of Total Daily Use
Showers 11.6 16.8%
Clothes Washers 15.0 21.7%
Dishwashers 1.0 1.4%
Toilets 18.5 26.7%
Baths 1.2 1.7%
Leaks 9.5 13.7%
Faucets 10.9 15.7%
Other Domestic Uses 1.6 2.2%

Interesting data, but I don’t think we actually use 69.3 gallons in a day. And certainly we don’t as this is an average across a large sample of america rather than a particular use case.  For example, in our simple environment, leaks should be negligible, and in fact, given how precious water may well be at least in some areas where the studio may live, a leak should be rapidly remedied.  This will become harder as a larger dwelling is added into the environment, and as larger water storage tanks are sunk into the ground, leaks in those tanks will be quite difficult to detect.

As an analysis of the “weekend” studio use case, which is the most likely initial case in this environment, we can remove the clothes washer and leaks and baths, but the rest we’ll have to leave until we can get either more data, or get some actual usage statistics longer term.  Originally I had planned on getting 1-200 gallons of water storage onto the site, thinking that would last a couple of weekends.  But this data has me re-evaluating that.  Now it looks like we should plan on ~30 gallons per person per day as an average.  That means that 200 gallons would only last ~3.5 days for two people!

As I had planned on possibly bringing in water when we visit (100 gallons at 8.5#/gallon = 850# extra in the vehicle, which it can handle), we could keep the tanks topped off for a weekend, and would be able to have friends stay the night as well.

Or we go to plan b: bigger tanks, and rain catchment sooner.  I will have to add a task to include a larger storage tank, perhaps of the ~1000 gallon scale, and get the water catchment up and running as soon as I get some roof-top space to start catching water on :-D.  This has re-arranged my plans a bit, as february and march are the wettest months in northern california, it would be nice to actually catch some rain.  Having a larger tank will also help, as it will allow for the possibility of having water delivered at larger than 100 gallon inputs.

So how much rain might we capture?  Going off of city-data.com data, January, February, and March see on average 5″ of rain, April drops to 2″, and May is around 1″.  So if we can get the catchment up and catch from both containers roofs, or a single 40’r (still wondering about that option), we have 320^2 of catch space, and 7.5 gallons/^3 foot of water, and if we get the average rainfall:

((feb+mar+apr+may)/12)*320*7.5 = ((5+5+2+1)/12)*320*7.5 = 2600 gallons.

If we were to go up every weekend, and consume 120 gallons per weekend, the 2600 gallons we captured would last 5 months with us there every weekend, or 10 months on alternate weekends.  But we’d have to capture it all.

And Plastic-Mart has 2500 gallon water tanks on sale for only $790!  Which we’d then have to ship from Florida…

Oh, an I shouldn’t forget about the extra ~16^2 of catchment on the tank itself!  Let’s see, that’s ((5+5+2+1)/12)*49*7.5 = 398 gallons!  Or another 3 weekends.

So we could potentially go up every-other weekend for a year (and I’m not even including the fact that it likely rains starting in September (1″, 2″ in Oct, 4″ in Nov, 5″ in Dec…).

So water catchment, at least with the current average rainfall could cover a couple’s weekend average water consumption needs on alternating weekends.  Good data, and now it looks like I need to find a local source for a 2500 gallon stock tank (oh, and I owe Mike an appology, as I told him the only way to get reasonable large capacity was to pour in place  a concrete cistern…).

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