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Water Catchment question  RSS feed

 
Kathleen Sanderson
Posts: 995
Location: Near Klamath Falls, Oregon
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I'm trying to choose between moving back to New Hampshire and living with my middle daughter and her husband (we'd build an apartment on a property they have yet to buy) and buying a couple of acres here and building a cabin.  I really prefer the latter option, but am not yet sure what's going to happen.

If we do stay here and build a cabin, though, I probably won't have enough money for a well this year.  I've done the haul water from elsewhere thing before and would rather not do too much of that again, at least not long-term.  My concern with catching precipitation on the roof and storing it is that much of our precipitation comes in the form of snow.  Our summers are extremely dry, and the spring and fall rains don't last long, sandwiched in between winter snows and summer drought.  Total average precipitation in this area is only about 17", and at least half of that comes as snow.  How is this going to work with a water collection and storage system?  It seems like most of the snow will just slide off the roof, rather than ending up in a storage tank.  That will leave me with a lot less precipitation to count on, and I'll need a lot more roof collection area to provide enough water to get through the summer drought.  Any thoughts?

Kathleen
 
Nicola Marchi
Posts: 79
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Roof steepness is what determines whether or not the snow will fall off the roof, I don't remember the ideal slope unfortunately but I can tell you that unless you install an active system to melt the snow, it will probably undergo sublimation and you won't see much of it at all.

Sublimation is when Ice evaporates directly and people generally see it happening over long cold stretches where new snow doesn't fall yet the depth of the snow slowly decreases.

If I remember correctly the way that earthships countered this problem was by installing solar water heaters and a Photovoltaic panel attached to a pump, so that they could circulate a liquid just under the roof skin and have the snow melt into their collection.

Considering the average american consumes about 45 thousand gallons of water a year, by themselves with no added animal or plant included, that would mean your cabin would need either 4.5 thousand square feet of catchment if you used a similar active system, or 9 thousand square feet of catchment if you had to go by rain alone.

Many people can and do survive on much less than that amount of water, and if you want to do your own calculations, just remember that 1 square foot of catchment provides .623 gallons per inch of rainfall.

Also remember, if you're calculating how much water you will need, that we almost always are using much more water than we actually need to, and if you were cautious and aware you could live on a few thousand gallons, bathing only once a week or so. On the other hand, you have to realise that most people make optimistic calculations and fail to keep up with their predictions.
 
John Polk
steward
Posts: 8019
Location: Currently in Lake Stevens, WA. Home in Spokane
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I believe that the estimate of 45,000 gallons per year is based on wasteful city lifestyles such as letting the water run while brushing teeth, and maintaining a lawn.

Realistically, we can live comfortably on less than 10% of that.  A good greywater system can further reduce usage.

Adding catchments to all roof structures can add significantly to the catchment.  An 8 x 10 wood shed will capture 50 gallons with each inch of rain.
 
Kathleen Sanderson
Posts: 995
Location: Near Klamath Falls, Oregon
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Thanks.  I *know* we can live on a lot less than 246 gallons of water per day per person, LOL!   I'm talking about a tiny off-grid cabin here, not a big house with lots of appliances!  I do have dairy goats and some poultry and a couple of dogs (one big and the other one getting bigger every day).  But right now the animals take a total of about 12 gallons of water per day.  My daughter and I could do fine on ten gallons per day for the two of us, except for doing laundry.  (Which I will be doing by hand, so add another ten to twenty gallons for that, once a week.)  Not including watering a garden -- definitely no lawn, we'll make do with the native sagebrush -- that comes to an average of maybe 25 gallons per day for us and the animals.  Annual total of 9,125 gallons.  I would need some water for the vegetable garden and for getting trees and perennials started, too. 

So, say I wanted to catch a total of 15,000 gallons (estimating high just to be on the safe side).  Trying to be conservative, I'll guess that about seven inches of our annual precip. falls as rain, so we'd need 1,335 s.f. of roof area to collect that much water.  Then I'd need to figure out how big of a cistern we'd need to hold that much (although we probably wouldn't need to hold all of it at one time, and in the winter a lot of the time I could melt snow). 

Kathleen
 
Nicola Marchi
Posts: 79
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Cistern Sizing is a somewhat complicated topic.

While with cisterns bigger is almost always better, the ideal cistern size is one that carries you through the dry months.

So theoretically if you got 7 inches of rain from September to March, you would need a cistern large enough to keep you full of water from March to September. At your estimated 15,000 gallons 7/12ths of that would be 8750 gallons.

An engineered cistern size would be a much more complicated process that would look at weather data and graphed water use with inflation for the summer months... I barely remember when I studied it a few years ago.

Another important topic is the roof material and orientation.

Ideally you would have a metal roof you're catching water, it gives both the cleanest water from runoff, it absorbs no water, and it's extremely long lasting when set up right. If you orient your roof south, the sun will melt at least some of the snow, and give you a surplus of water.
 
Fred Winsol
Posts: 155
Location: Sierras
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I live in snow country in California... it doesn't rain from April - October... and I have lived for 8 years with 100% rainwater... it was new construction... i designed a 4000 sqft steel roof with 500 gallon cistern and then pump it up with PV pumps to 25,000 gallon tanks up the hill and then it's gravity feed all year long.

i love it... would never go back from rainwater... it's soft and free.

Retrofit would be to assess roof and tank size.  There's standard calculations for cisterns based on household needs and annual rainfall... google them.

 
Kathleen Sanderson
Posts: 995
Location: Near Klamath Falls, Oregon
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Our rains taper off in mid-June, usually, and then all we'll get is a passing thunderstorm or two until sometime in October.  I think most of our rain falls in the spring (which tends to be wet and chilly) -- that's handy for keeping a tank full for summer use!

Kathleen
 
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