Harvest time – 2, (water harvesting, that is)

A couple of years ago I posted a piece about my water harvesting setup. I just read it through and realise that for most people it is much more complicated than necessary. I want to describe a relatively simple way to increase water storage, based on part of my system.

Sue’s glasshouse has a footprint of 18.25m2. Our annual rainfall is 1350mm, so the glasshouse roof could potentially collect 18.25 x 1350 = 24,637.5 litres. That’s a lot of water.

There is an integral gutter down both sides of the glasshouse and with the wisdom of hindsight I would have constructed the glasshouse with a slight fall, perhaps 1:500, front to back. For many years the gutter on one side was open both ends and the water ran out into tub trugs at both ends. On the other side it was blocked at the back and at the front ran via a length of pipe into a 230L water barrel a meter or so away from the glasshouse. The barrel had a tap but we usually dunked a watering can in the top. The pipe was a Heath Robinson affair and being at gutter height (1.38m, 41 6”) we walked into it all too frequently.

When I built an extension onto the glasshouse in 2021 I was determined to improve things. The low flying pipe had to go and the storage volume needed to increase as the barrel was quickly emptied in summer.

Glasshouse waterworks layout.

I put a water barrel at one rear corner of the glasshouse with the flow from the gutters feeding into it. A length of aluminium profile carries the water across the rear end of the house. I kept the lid provided with the barrel and made holes just big enough to feed the water into it. To the tap take off I connected a 20mm LDPE (low density poly-ethylene) pipe which runs along the side of the glasshouse, just below ground, to join the original water barrel located conveniently a few feet from the glasshouse door. Rainfall feeds into one barrel and via the connecting pipe, fills them both. When a can-full is scooped from the front barrel, it is replenished from the back barrel. The water level in the two barrels always remains the same. All I need to do is keep the gutters clean and we get an excellent supply of clean rainwater.

Both barrels have to be at the same level but while the collecting one probably needs to be adjacent to the glasshouse or whatever other water source you have, the second barrel could go anywhere. Furthermore, put a tee into the connecting pipe and you could connect any number of additional barrels and position them wherever is most suitable.

Alternatively you could have multiple collecting barrels feeding into a common pipe and whatever storage you chose. You could for example, have small, slimline water butts on a number of downpipes from your house gutters and feed them into a large storage tank behind the garage which has a submersible pump permanently in it. Once the pipe connections are made the water level will be the same across the system. It made be sensible to have valves in the pipe network so parts can be isolated, or you could have taps to draw water off at any point.

It may be that adjacent to a house you have hard surfaces that make burying pipes impractical. I connect one collecting water butt to my main storage with a hose; both butt and storage have quick click connectors and isolating valves. When the rain stops I put the hose away. It’s much easier than pumping the collected water.

Ldpe pipe is connected with barbed fittings and I would suggest using fittings that have a locking mechanism for the joint. Without them the joints tend to leak or come apart. You will need to heat the pipe to get it onto the fitting, dipping in hot water does the job. It is a simple system to install and not expensive, and the payback in terms of water saving if you’re on a meter, and convenience in having water just where you need it, makes it very worthwhile.

6 thoughts on “Harvest time – 2, (water harvesting, that is)

  1. The water collection system you made is exactly what I did in my greenhouse 5 years ago and it works great.
    A barrel outside which collects the water from the gutters and which transmits the water directly to another one : the levels are balanced and you can close the system for cleaning, or add others. The only difference between you and me is that I have one barrel inside and one outside. I had to pass my pipe under the foundations of the greenhouse: At this place I have 500 + 350L.


  2. Great to see someone else catching water! We installed four large tanks three years ago catching the water from one side of our roof, but we have them plumbed into our dishwasher and washing machine, as the principal reason for the tanks was to enable our household to go on running if the city ran out of water altogether. We also have a system that stores the water used by the washing machine and puts that on the garden — not all the plants like the rather soapy stuff, but most seem to manage. We can attach a hose pipe to our large tanks and use that to fill the pool or water the garden, though we usually don’t have enough to do so. I’d like to install some more tanks to catch the water from the other side of the house’s roof, but it is all rather expensive or time-consuming, if you do it yourself…


    1. Water is not generally in short supply here but ours is metered so there is an incentive to reduce usage. I aim to store enough to keep the garden watered in summer, mainly the things in pots, without drawing on mains water. It would cost far more than we’d save to collect the water we use in the house and there are other things I could do that would be of more environmental value. Water storage takes up a lot of space too, where I could be growing something.


      1. I had not realised that anyone had unmetered water. It was only reading allotment blogs that I came across the idea. But, yes, water storage does take up space…


      2. Historically here, water rates were part of local government taxation, then water supply was privatised and the water companies were encouraged to get supplies metered. They’ve never finished the job of installing meters, in our area 79% are on meters. In about half the country less than half of households are metered.

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