DIY Water Harvesting With Self Cleaning Filter

There are plenty of devices available on the market for harvesting rainwater, but there are very few ways you can do it without an expensive part bought from the store. This system is designed to be implemented with stuff you probably already have, or can get cheap.

The cheapest way to harvest rainwater is to direct it straight to your collecting barrels. But that has one very important problem: Your water barrel gets dirty, it soon contains enough pollen & leaves to start smelling very bad. That's why it's important for your water harvesting system to have some sort of a filter. Last summer my water barrels truly stank, so this year I wanted to figure out something better.

There is also a second problem in directing the water straight to your tank: what happens when the tank is full? It might not be a problem if you don't get much rain, but for me the water would outflow to the back wall of my garden shed.

1. Pipe (I used a leftover gutter pipe)
2. Angle part to attach to the pipe (anything between 45 or 90 degrees is fine)
3. Pantyhose for filtering.
4. String or wire to attach the pantyhose.
5. A big bowl or vat for gathering the runoff. I had an old rainwater funnel that I used.

1. I detached my downspout from the roof guttering, and attached it about 50 cm lower. I obviously had to remove the same amount of pipe from my downspout.
2. I attached my rainwater funnel (the big black plastic bowl looking thing) into the downpipe to gather the runoff. You can use any old bowl to do this, just make a hole in the bottom, and attach it to your downpipe. If it's a plastic bowl, I would recommend using a hot air gun to melt the bottom to match inner diameter of the pipe.
3. I added the diverting pipe. I made it by adding a 45 degree angle to a pipe. Your harvesting surface should be a bit bigger than the size of your downspout, so if your pipe is the same size or smaller, you can attach a funnel part to it to increase the water inlet size.
4. Finally I attached the pantyhose. You can use any old wire or string to keep it in place.

When water comes down from the gutter, it enters the harvesting pipe. If there is debris in the filter, the incoming water cleans the debris and it falls into the vat, and is delivered where your roof water would normally go.

When your water tank is full, the rest of the water automatically goes down the drain, if you've attached the harvesting pipe to your water barrel at the correct level. I didn't have that option, so my barrels also have an extra pipe that the water flows out if the tank is full.

Since I live in Finland, there is also the winter to think about. This system is easy to prepare for freezing temperatures, all I need to do is to push off the harvesting pipe (see last image).

The efficiency of the water harvesting depends on the filter used, and on how much of the water directly fall into your harvesting pipe. I haven't done any measurements, but it looks to be fairly efficient - not much of the water is wasted.

Unfortunately the pantyhose doesn't filter out all of the pollen, so if you need to drink the water, you will need a better filtering system. But it does seem to filter out most of the pollen, and all of the leaves / pine needles! And best of all, you can probably build it from parts you already have.

Have you implemented something similar, or do you have suggestion for improving it? I'm interested in hearing about it!