Rainwater Harvesting & Micro Hydroelectric

Last updated on April 28th, 2024

Pipe dream, yes pun intended, or coming to a gutter near you soon. Turns out some people from Exeter University have done the math and micro-hydroelectric generators in downpipes could be a thing.

image from MDPI Open Access Journals

Schematic showing concept of generating and storing electricity from rain fall

Rainwater harvesting has been on my mind since I started cleaning gutters when I began to see better-designed water butts other than the old big barrel I grew up knowing. Many more aesthetic, interconnected and space-saving designs exist. A few are listed on this page.

However, what’s more exciting is the research being done to convert the rainfall into electricity using the existing gutter system. To a gutter cleaner like me, that is exciting stuff. Not solely because this would surely lead to an increase in gutter cleaning if technology like this was implemented, but more to do with, that it seems obvious. Especially, when the world of home power walls comes to fruition. I’m starting to understand the figures but a closed-loop system using the guttering system to harvest rainfall & its energy just seems right.

Of course, there’s more math and engineering that I don’t understand but the sooner we start capturing and diverting rainwater to flush toilets rather than using treated water then the net gains would be significant across the board. That’s even before trying to convert any rainfall collection into electricity to power the loop and potentially other small devices. For instance, a large aesthetically pleasing water butt like the ones below could be used to store harvested rain water. A small pump and battery to fill the cistern when required. This doesn’t seem too expensive or hard to implement from a DIY or professional installation (do I win a million pounds).


Let’s do some pub maths

Let’s say a household has a 200-litre storage tank and the average flush is 10 litres for ease and the average from those households is 10 times a day. Well, that’s two days’ worth of flushing right off the bat and let’s say you could accomplish this 2 days of each month that’s 24 days in a year. Even though I’m just plucking figures out of the air I’m sure starting in Cardiff that figure could be achieved. see rainfall stats here.

In the chain of water treatment for every litre of rainwater used you’re saving 1 treatment of clean water from not being used, and 1 treatment of rainwater being unnecessarily treated if that rainwater was already heading to the combined drain. Therefore the 1 litre of your flush water is twice as cost effective. Get a million homes doing this and it may be enough to prevent water treatment works from dumping raw sewage into the rivers and seas. Is a million households not enough? then do 2 million… You get my point, no, have some more beer or better still add some comments below.


Infrastructure changes – none

Nothing changes here; storage tanks, check. Those million houses may have some already or could buy one tomorrow. Better still make it a government scheme. Need more storage tanks; build some more using recycled plastics, check that’s a win-win.

A small pump and a bit of simple plumbing to get to the cistern, check . Again, all are readily available parts and water pumps use very small amounts of energy. The next stage would be using the rainfall energy to keep the battery topped up to keep powering the pump, check.

Some mechanism and pipe holes in the cistern so it can fill from the rain tank and switch when empty, check. Ah pub maths, where you do not have to have all the details, check .


To me, this seems simple in almost every aspect, except the plumbing into the cistern and switch but again I’m sure the solution will be to use existing parts. Implementing this not only creates a bit of work for various trades due to a relatively simple installation anyone could take it on. It is, however, the knock-on effects that pay the dividend.

Not using a resource like rain that is delivered to your house for free, letting it flow away, to then use electricity and manpower to treat it, then pump it back to its origin, just to flush it away again seems like we missed a page.

Even without government funding a million households could pretty much have some version of this implemented tomorrow. Make it into a design competition with a prize and boom! job done. Move on to the next problem, you’re welcome

To Sum – Clean Gutters Required

The best thing about this is you need to keep your gutters clean. To maximise that lovely rainfall and energy. You can’t have your gutters blocked or even partially restrict flow as that will impact your harvesting and energy production. Gutters cleaned every week!


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