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Gravity fed water for Milkwood Farm

February 28, 2011 | Water Harvesting + Reuse | 15 comments | Author:

One of the most powerful concepts in permaculture for me is ‘keep the water high’. All water stored high in the landscape is potential energy, thanks in part to gravity. If your water is high, you can make that water available to everything below it in the landscape, via gravity feed and piping, with no energy spent on pumps. At all. Which makes for one resilient landscape.

So when it came to designing the rainwater harvesting for our drinking water at Milkwood Farm, we knew we wanted to store the water high. This way, if we didn’t have power for some reason, we would still have drinking water at our house, because we wouldn’t be relying on a pump to deliver the water to us. But we aren’t building our home on top of the hill – so how to get the water up there?

Loading one of our stainless steel tanks onto the truck for its final ride up the hill to our shed

Most farms I’ve been to harvest rainwater off the roof of the house and/or nearby sheds, and store it in tanks nearby. Then the water is either pumped directly into the taps from there, or pumped uphill to a header tank. From there, the water is passively gravity-fed back down to the house’s taps.

In this kind of system, if the pump fails or the power goes out, you have no water until you fix the problem. Which means your drinking supply is completely dependent on that pump.

Up and past the woolshed - watch those overhead power lines!

We were originally planning to put a tank next to our tinyhouse, catch water off the roof, and use some sort of solar pumping system to pump the water up the hill to a tank and gravity feed it down from there. This plan presented three problems:

  1. A tinyhouse has, by association, a tiny roof. This means not much catchment area. Which would be fine in the subtropics with regular rain, but not such a good idea where we are with our temperate, variable rainfall
  2. We would be depending on mechanical parts to ensure we have drinking water, which is a risk. What if the pump breaks? What happens in the meantime until we can fix or replace it?
  3. A solar pump pumps water uphill a little at a time, slowly. So if we had a big downpour, our house tank would overflow before we could get all that water up the hill. Which means we would loose some of the precious rainwater. And i want all the rainwater i can possibly catch, for that non-rainy day – or month, or year…
Rolling the second tank off the truck and into position - surprisingly easy, so long as you take it slow and get some friends to help

Once we looked into the cost of a house tank, a solar pump, a header tank, and the plumbing between them, we realized just how expensive this factor was going to be. Ouch! Was this really an efficient use of energy and funds?

Instead, we decided to design a rainwater harvesting system that sat high in the landscape, caught more water than we could ever use in a year on our farm, provided passive gravity-fed water pressure to our house and buildings, and doubled as a big, useful undercover area on top of our ridge. In other words, we built a really big shed.

One tank in position and one to go, next to our super-duper catchment array (read: shed roof)

To cut a very long story short on the shed front, we salvaged the structural components of a big shed from a junkyard, prepped them, put them up, got some end-of-the-line roofing iron, and before we knew it, we had a really big shed roof on top of our hill. 260 square meters of rain water catchment. Yeehar!

Next we needed something to store the water in. After a long-winded research period, as outlined in Water tank comparisons for drinking water: defining clean and green, we decided on stainless steel water tanks, as they gave us the highest quality drinking water and were completely re-usable at the end of their life.

Just...don't...drop...it...

It was a great and exciting day as we moved the water tanks from their resting place at the farm next door (they were delivered before the shed was built) and then drove them up, up the hill and positioned them proudly on the western side of our shed.

And the final positioning push...

That afternoon we put a bit of water in the bottom of the tanks to stabilize them (wouldn’t want them to blow away before they filled with water, after all that effort), and at time of writing the rain is pattering down, the shed roof is catching it and our drinking water supply at Milkwood is beginning to exist.  Yay for water resilience!

Stainless steel rainwater tanks! On the highest point of Milkwood! With bonus shed!

It’s true we don’t actually have a tap to drink that rainwater out of quite yet, given that the tinyhouse is still being built. But it’s only a matter of time. And one fine day soon, when it’s all done, when I finally turn a tap on in my very own kitchen, to fill a cup to give to my little boy to drink, I am going to be one proud, gravity-fed, rainwater-drinking mumma.


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  • http://www.allyoucaneatgardens.com.au Tim Auld

    Thanks for the story, that’s a nice shed and rainwater harvesting system! Do you have plans for the overflow of these tanks – it would be a significant flow of water!

    I wouldn’t say someone with a house tank and pump is completely dependent on the pump for drinking water. You can add a non-pumped tap to the tank and bucket the water. Depending on the height of the tank you might also be able to get low pressure water through the tap when the tank is full enough.

    The sub-tropics can go for periods without rain too, so tank size is still important there.

  • Kent

    Congratulations! I hope you get a nice bit of rain now to get them filling.
    That first glass of water is really rewarding. My favourite harvested-rainwater-moment was the first soak in the bath… SO indulgent!

  • http://ecofootprintsa.blogspot.com Dani

    Lovely tanks – and nice and big! Expensive compared to the others on offer? Are you going to sterilize the rainwater before letting your little one have some? (http://www.newton.dep.anl.gov/askasci/wea00/wea00044.htm)

    Could definitely use some of those on our smallholding :-)

    • http://milkwood.net milkwoodkirsten

      Hi Dani,

      Nope, we will be drinking the rainwater without sterilization… Apart from the fact that ‘town water’ is not an option where we are anyway, we are very comfortable with drinking rainwater (which is what everyone else drinks anyway) without it going through a bunch of pipes and chemical processes…

  • Julie McDonald

    Hi, Where did you purchase your stainless steel water tank? I am in the Mudgee region.
    Cheers
    Julie

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  • CW

    Is there a time limit on how long water can be in a tank before it loses potability ?
    I’m looking to apply this in the humid tropics i.e. catch in rainy season, use in dry ( 6 months).
    Lots of talk about algae etc…. Your thoughts would be appreciated thanks !

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  • Clare

    Hi
    Like this system. We are wanting to do some similiar. Looking for resources on how to connect the tank to a cottage some distance away. We already have a large tank and shed on our ridge.
    Cheers
    Clare

  • Ken McBryde

    HI Kirsten,

    We are finally going to put a house on our farm (just shed with inbuilt accommodation so far and we are not yet living there permanently). Shed has 180 m2 of roof so pretty good and a 45,000 litre concrete tank with pressure pump. Works ok – but …

    Have always liked the idea of getting the tank/s higher and gravity fed to house when no power etc. so will try to implement that in the new house set up. That’s the header tank system you mentioned – for us that would mean using a transfer pump to pump from a smaller collection tank to the larger storage system up on the hill. My question is what vertical height above the house do you have to install the tanks so as to get good water pressure at the house? Are you happy with yours or would you try and get the tanks higher up?
    regards
    Ken

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