My rainwater harvesting installation
My rainwater harvesting installation may have jinxed the weather!
Ever since I’ve finished installing my new rainwater harvesting installation in my garden here in South Somerset it has rained almost every day!
We have had just so much rain! In fact so much rain that I haven’t had to use a drop of the rainwater stored in the large tank!
Why install it?
We had builders on site adding an extension to our home throughout much of Covid 19 lockdown. That work over-ran and material prices for the project went off the scale.
But having a builder on site was the perfect time to lay pipework to capture rain falling onto most of the roofs of our property.
For sometime that gathered rainwater just ran to waste but eventually we ordered and had delivered a whole rainwater harvesting system.
In the future I’m sure that water will become much more of a limited and more expensive resource.
At the current cost of tap water it will take many years to pay off my investment in my rainwater harvesting installation.
I’m convinced that plants watered with rainwater grow better than those watered with water from the mains supply.
It is a shame that such harvesting systems are not yet mandatory with all new build houses.
What is it?
The system consists of a very large durable tank, a system for filtration and a submersible pump. Connected to this is simple supply pipework and standpipes.
Now I’m not the best person to do DIY and so I was happy enough to employ a plumber to fit everything together.
I also wanted to be sure that the fittings were appropriate, durable and and wouldn’t leak!
So I confined myself to digging a suitable large hole near the lowest part of our garden but also near to a power source in our garage.
The storage tank
The 3,000 litre capacity storage tank needed a big hole!

Rainwater tank, piping and standpipe
Most of the tank is below ground level now with only the dome turret and lid protruding above ground.
The German made Graf tank is lozenge shaped and is of rather complex construction.
There are voids in the tank that needed to be filled with rounded gravel.
These columns, when filled, provide significant extra strength to the tank and laid in the right way can bear the weight of vehicles driven over the top!
Please ignore the dustbin lid I’ve left on the top to temporarily keep the electrics dry!
The pump
Suspended by chains into the tank is a Divertron submersible pump from DAB Water Technology.
This pump pressurizes a pipework system that I’ve installed throughout the garden.
This means we have rainwater for irrigation throughout all of our garden.
By turning a standpipe on the pump detects a drop in pressure and starts up to pressurize the system again.
The submersible pump has a float switch that will cut the pump out if water levels in the tank drops too low.
Filtration
When the rainwater enters the tank it flows into a basket filter.

Filter basket with pump below
This should catch leaf litter from nearby trees which will inevitably be on the roofs.
Our roofs also grow a lot of moss and from time to time this peels off and ends up in the gutter.
I already regularly clean the roof gutters but now I must remember to empty the basket filter!
Without this filtration the tank would gradually fill up with rubbish.
The supply system
We have four standpipes to which we can attach hose pipes or fill cans.
As I’ve already said, I’m convinced that plants watered with rainwater grow better than those watered from the mains supply.
One of the standpipes will also be used for car washing.
We are fortunate in that there is a steady fall from the top of our garden to the water storage tank.

Drain valve to empty system in winter
I had the plumbers fit a drain valve at the lowest point to drain the water from the standpipes and pipework that supplies them.
This will be especially important during frosty weather.
In fact, since I only use a little water in the greenhouse and polytunnels during winter, I will drain all the water out of the pipework in late autumn.
Come spring it will be easy to fire the system up again.
Further plans
It is my intention to connect soaker hose irrigation pipes to the standpipe nearest to our fruit cage.
Even though the summer of 2024 has been mostly wet the yield of raspberries in particular was lower than expected. At times I resorted to watering these raspberry canes with mains water as they frequently showed symptoms of water stress. Raspberries are quite shallow rooted and perhaps they will benefit most from a regular supply of water from my rainwater harvesting system.
It may be that the large 3000 litre tank will not provide us with enough water for our large garden.
With that in mind I am prepared, if necessary, to instal water butts on some of the key downpipes. When those butts are full the excess water will then go into the large Graf tank.
Hiding the tank
The tank is not a pretty thing. Being mostly buried I am confident that I can hide it further by encouraging scrambling plants to cover it.

Muehlenbeckia complexa
I already have a small Muelenbeckia complexa established on one side of the tank. It is steadily growing over the tank. This very small leaf scrambling plant from South America is often seen planted in winter patio pots and hanging baskets. However, once established it can become a bit of a thug. The tank is close to one of our native hedges and I must be sure to prune any bits of this plant that escapes into that!

Hedera colchica Dentata ivy
Muelenbeckia comes from South America and planted in the lowest part of our garden I am a little worried that a hard winter might kill it.
So I plan to establish the large leaf Persian ivy to screen the tank too. I have in mind using the unvariegated form Hedera colchica ‘Dentata’. This is less commonly available but, being not variegated, is more vigorous than the widely available variegated form of Persian ivy.
I will allow both the Muelenbeckia and Persian ivy to scramble over the tank without any support.
Advice and supply
Landscape Plus gave me great advice and guidance and I ordered my rainwater harvesting installation from them.
They have considerable experience in the supply and installation of rainwater systems. I’d recommend using them!
Further Reading
I visited Oregon, USA again this summer. I was impressed with the use of water bags to improve establishment of young trees there. You might be interested to read about that here.
I’m always impressed by the wide use of SUDs when I visit Portland, Oregon. I’ve written a blog about this increasingly important method of controlling water run-off in cities here.
In Scotland I was inspired to write a blog about green roofs.
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