Wednesday, October 14, 2015

water collection

Finally made some progress in capturing and storing rainwater. The north half of the barn roof now flows in to a 350 gal. ( 1325 l) tank, and I have installed a gravity driven drip system to our fruit and nut trees downhill of the barn. 

The routing might look goofy, but I was trying to place supports that tied in to the internal structural, find a level spot, keep the tank on the north side where sunlight ( causes algae) is minimized, as well as not being below the window.  

This is still not enough capture, so I plan to expand the storage to catch even more of the rainwater. Plans for the south roof flow are to irrigate the south garden. When I get that side finished I'll post an update with photos as well. 

Barn is 30 ft. ( 9m) x 60 ft. (18m), so a 1 inch (25mm) rainfall will provide 150 cubic feet, ( 4.25 m3) or 1100 gallons (4200 l)

Since each downspout is catching half the roof, this setup could potentially get 550 gallons (2100 l) from each inch of rain.

Average annual rainfall for here is 36.56 in. ( 928mm), which is a generous amount of rain, so I really just want to save enough to get through drought stretches as long as this setup is just for trees and supplementing rain in the veg gardens. 

If we decide to try to rely on rain for more uses, and the well pump for less, then the need is a great deal larger. For now, I plan to increase storage enough to capture rain from April through August, which is about 17.6 in ( 450mm). That's a lot, but I would stay with above ground storage, and simply drain and shut down in the winter. 

If we try for year round use and storage, then insulation or an in gound cistern will be needed. 

The drip system has had some problems to consider. First, it was hard to find components that are suitable for low pressure . Many catalogues have "low pressure" fittings, but this means 5-15 psi ( 35 kPa- 105 kPa). Since I am using only gravity, I have much less than than, somewhere in the order of 5-15 feet of head. I found some that are marginal, but the flow is still not very good.

Second, running it above ground means that once grass and weeds grow up, it is hard to find! I put out a few flags, but need to do some more to make sure we don't damage it and can find it if maintenance is needed.

Third- It will be hard to drain all the way before freezing temps arrive, without taking it all up and coiling it. I may try to blow it out with air.

I got this finished late in the season, but it should really give the trees a boost next year.


  1. Hi Steve,

    Top work. Incidentally, the water stored can be used for drinking water purposes if the power goes out. If you are not near a major city - or major electrical generator or other such industry, the quality of the water should be pretty good.

    Incidentally, using gravity, the trick here is to use wider diameter pipes so that the friction is lower. For gravity pipes here you can readily purchase 1 inch or 2 inch UV stable poly pipe and the flow rate from that is pretty good. Also we have low pressure water sprinklers which work on gravity alone - they're very good.

    Cheers. Chris

    1. I have also experimented with gravity-fed low-pressure drippers. I've since pretty much abandoned this idea.

      I had about 1 - 2 m head of pressure (similar to you), and was able to get the drippers to drip just fine. What I found was that small differences in elevation of the drippers made an enormous difference to flow. The drippers that were slightly (20 cm?) lower were getting nearly all of the water, while the higher drippers were getting almost none (a few drops). This could have been partly due to the way I routed the piping, and was mitigated when I added extra connections between vege beds (I was only using 13mm pipe, so friction losses would have contributed). Also, it was impossible to know how much water was being used, leading to over-watering in places and under-watering in others.

      I'm now transitioning to wicking beds in the hope that I can get better water efficiency.

      I like your blog -- please keep sharing.

      Cheers, Angus

    2. Hadn't heard of wicking beds, but the concept makes sense for some situations. In the case of my current setup, I'm spot watering existing trees, each being a young fruit tree with a bit of mulch around it.

      The wicking concept would be hard to retrofit, but it reminds me of a similar thing we are doing with container gardening. A false bottom and a reservoir in a plastic container enables efficient watering without anaerobic conditions setting up. Water wicks up to the plants through the potting soil. It's especially helpful if you are going to be gone ( or forget!) for a couple weeks.

      We have been keeping herbs and flowers going through the winter in our sunroom for four years now. (Winters here can get down to -20F/-28C, so many perennials can't make it without a little help)

      A link to a similar arrangement to what we are going.
      A google search on "self watering container gardening" will bring back all kinds of variations on this.
      ( I guess I need to do a post on ours)

  2. Chis- Yes, I plan in the future to use it for drinking water, and yes, we are miles from concentrated air pollution.

    I'm familiar with friction loss, I think the HDPE ( high density polyethylene) tubing I have is big enough and working fine, it's the emitters at the very end that are not well suited. They need a higher pressure to get reasonable flow. I might just drill them out a bit. What brand or manufacturer are the gravity sprinklers you use?

    Oh, another future project will be to capture and utilize rain off the house roof. That will be trickier, since the house is down hill from our gardening, trees, and animal locations.

    Thanks again for comments.

  3. Hi Steve,

    Always a pleasure! They make the low pressure sprinklers down here: LOW PRESSURE COUNTRY SPRINKLER and they work with just gravity pressure - it is a very impressive sprinkler. Sometimes they call them a wobble tee sprinkler.

    Fair enough with the roof capture too. Down here in such a situation, they collect the water from the roof in a small tank and as it fills that water is then pumped up to a higher level tank and gravity fed back downhill again. Otherwise, a pump is connected to the water tank at the house and the water is pumped up the hill. Generally moving water uphill 20m (66 foot) is fairly easy on an energy front. For that sort of purpose a 17L/min (4.5 gallon/min) 60psi pump will do the job no dramas. Beyond that height though, you'll need a much bigger pump.