If you grow plants and have access to a gutter downpipe, it’s well worth finding the space and time for a water butt. Rainwater is better for your plants than tap water*; and of course you help conserve water as well.
For small spaces you can get slimline water butts; we have room for a 250l one, and it’s worked out very well. This weekend was the first time this year I’ve needed to fill the watering can from the tap. I did put off fitting it for ages, but in fact it was an easier job than I had feared.
You’ll need a downpipe diverter, and a hacksaw to chop through the downpipe. The diverter kit will have detailed instructions, but basically you cut through the drainpipe at a height just below the top of the water butt. You then connect diverter and water butt with a piece of tubing, and when the water in the butt reaches the level of the drainpipe, the water will flow back into the drainpipe and down the drain. (Here’s a basic explanation of the physics of how water finds its own level; imagine the drainpipe, which is ‘bottomless’, as one of the tubes, and the water butt as the other, with the tubing connecting them.)
A note: when measuring the height of your water butt, it is VERY IMPORTANT to place the water butt high enough off the ground that you can get a watering can in under its tap. We used spare paving slabs; you can also get a purpose-built plastic stand.
Once you’ve cut the drainpipe and fitted the diverter and its tube, that’s it — you’re done, and your water butt is ready to collect water the next time it rains.
The only problem we’ve found so far is that the angle between drainpipe and water butt means that our tubing has a couple of kinks in it that tend to gather gunk & allow algae to grow. This means that it needs to be cleaned out occasionally to keep the water flowing. We’ve just added gaffer tape to reduce the amount of light and thus hopefully also the algae.
Next job: fitting a smaller one on the front balcony. I need to check this with the neighbours first, though, as we share that drainpipe.
* If you can’t use rainwater for watering, when possible it’s a good idea to let tap water sit for 24 hrs before using it on your plants, to allow the chlorine to offgas.