Plants Need Water. But Harvesting Rainwater Without A Shed Roof or Greenhouse Sounds Impossible. Here’s How To Harvest The Rain Without a Roof.
Allotments need water but not everyone has a shed or greenhouse from which to harvest rain water. But don’t despair, there are plenty of rainwater harvesting tricks that will give you a good supply of water.
How Much Water Falls On Your Garden Each Year
In the UK we get an annual rainfall average of 33 inches across the country. Some of us will get a lot more, and some of us a bit less. Where I live we get 31.5 inches in the average year. That’s a lot of water.
An inch of rain is 22,610 gallons of rain per acre. It’s a huge amount of water. But of course it doesn’t always rain when we need the water, so we need to harvest and store it for when it is needed.
And let’s not forget that most gardens aren’t an acre so will get less rain then that. So what can we practically expect to be able to harvest?
But none of us gets just an inch of rain. We will all get more than one inch a year. As I said, I get 31.5 inches a year.
That’s an incredible 712,215 gallons an acre. It’s such a big figure its hard to visualise it. So what would it be per square yard?
Well there are 3840 square yards in an acre and that means each square yard of my garden gets 147 gallons of rain in the average year. It’s still a lot of water. It’s enough to fill a a 50 gallon water butt three times over.
I’m lucky enough to have a few IPC tanks for water storage. They are approx 275 gallons (1040 litres) each. So the rain from a square yard of garden will roughly half fill one of my tanks.
How Can I Harvest Rain Without a Roof?
So it’s clear that enough water falls in the average garden. But how can we collect it without a roof?
It’s actually simpler than most people imagine.
Rainwater that lands on an IBC tank normally runs off of it and falls to the ground. It’s wasted.
But what if you converted the top of the tank into a large funnel and divert the rainwater into it and collected it all? The surface area of my tanks are 1.3 square yards and have the potential to gather 191 gallons a year. And if I made the catchment funnel a bit bigger I’d catch more water. In fact if it were just 1.8 square yards it would just about fill the tank each year.
Of course we tend to use water over months, not a single day. So there is the potential to collect more water as it starts to empty. We can collect a multiple of the actual tank capacity.
The Reality Of IPC Funnel Rainwater Harvesting
The more water we want to collect the bigger the “funnel” we need on top of the tank. And it all gets a bit silly. We’ll soon have a funnel that overhangs the tanks and starts to get in the way.
But what if you had a temporary funnel? One that you could store when it’s not needed? You could deploy it when it rained and fold it up and store it at other times.
That isn’t such a silly idea as it sounds.
Temporary RainWater Harvesting Systems
If you were to string a canvas “sail” from four permanent posts in your garden, or allotment, and funnel the rainwater it catches into a tank, you could then store the sail away when you had enough water.
Here’s the design I recommend.
Install your posts so two on one side of the sail are higher than the two on the other side. The result will be a sloping sail that will catch water. And if you construct it with a “valley” in the middle the rain will run down it right into your catchment tank.
Of course the construction needs to be sturdy and it would be unwise to deploy it during hight winds or it will “sail” away. But used wisely you can gather a lot of water during a relatively short rain storm.
Why not give it a try?
There’s an article of rainwater harvesting, rainwater movement and storage via this link.
There are some great examples of rainwater harvesting systems on Wikipedia