How to collect rainwater for gardening


Currently illegal in Colorado.


I prefer my friend’s design that just uses an open barrel. She deals with the mosquito problem by putting in goldfish. The goldfish turn the mosquito larvae into fertilizer…okay, maybe not, but, hey, goldfish!


The article makes brief mention of mosquito larvae, but in fact this is a serious problem. The adults will find a way through the smallest gap and lay eggs, and a week or two later there will be new adults finding their way out the gaps.

Most rain collection surfaces will add enough organic matter to support a thriving microbiota, which then supports the filter-feeding larvae.


Oh, and rain.


IIRC you can float a small amount of (vegetable) oil on top of the barrel to make it unusable by mosquitoes. Whether this creates a home for other growth, I don’t know.

I’d be worried about anaerobic organisms. You might add an aeration tube and go the goldfish route instead.

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Sounds interesting. Where I grew up as a teen we collected rain water into a cistern for daily use because water (back in the '80s) cost like $0.15 a gallon in bulk from the Israeli built reverse-osmosis plant on the island.

We used screens over the overflow and filling tube, and regularly added clorox bleach in small amounts to the water. It was safe to drink, and I miss drinking rainwater, but you had to take military showers and only flush for #2.

Edit: the amount of bleach added was a couple of cap fulls at a time, done by my father, but was difficult and not done too often in a year, because access to effectively add the bleach to the water was under the pump, and the water was tested at that time as well.


the trouble with the goldfish route is that the lone rangers come out and get them.

Rather than get that hard-to-find Y connection and a valve, it makes more sense to just let all the downspout’s output to into the barrel, then have an overflow fitting for when the barrel’s full.

Bonus: when there’s enough water and more is coming in, all/most of the larvae will flow out the overflow.


Over here, you can get a ‘rainwater diverter kit’ that contains its own overflow. It only costs a few quid and takes a couple of minutes to splice into an existing drainpipe.

Since I did this last year, I always have a butt full of rainwater.

Just conceal the cisterns, e.g. inside a shed, and don’t ask a fucking bureaucrat for a fucking permit. The rainwater is a trespasser on your property anyway and deserves to be detained for a while. It’s not like it won’t be released back to the nature later anyway.


Where “illegal” means that you need to spend $60 on a permit. Which, admittedly, is pretty annoying and possibly more expensive than the materials.

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I completely agree.

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The container is an “IBC tote” which typically holds 1000 L and can be found used on Craigslist for about $80 USD.

I cut off the downspout and replaced it with 3" PVC pipe with a 3-in Diameter PVC Sanitary Tee Fitting to send the water out the side via a 2" pipe. I used a rubber leak patch hose as a flexible connector on the side pipe so it can move a bit

The downspout ends in one of these flexible downspout connectors which gets stuck into to top of the Tee fitting. There’s a hole drilled in so it can burp air.

The diverter is a “test cap” which blocks the bottom of the tee.I put a hole in the cap using a nibbler tool. This guy also put a hole in a test cap, but the hole in mine is 30% smaller.

The hole is blocked by a silicone toilet flapper. I can reach into the tee and pull the flapper when the tank is full.

The tote that is shown in the picture is not using the opening filled by the red plug that screws out of the big cap on top of the tote.

That’s a standard 2" pipe fitting, and that’s how my PVC pipe delivers the water to the tank. Knowing that, it would be easy to make a sturdy PVC funnel with a filter screen and overflow that could catch water from the existing downspout. I also built a flow through screen filter cartridge to divert out the trash, but that’s a different story.


It helps if you actually have rain! We’ve not had much here in Santa Cruz…

That what my rain barrel does. Cut the downspout to the height of the barrel. Water pours through screen into barrel, overflow at the back when it gets full in a rainstorm.

It’s good to have even in places with less drought than California, like Delaware, because there is always a few weeks in the summer when the vegetable garden could use some water, but the rainclouds have not provided. It is like a DVR for water, time shifting the rain to when I need it.

We get around the larva problem by having a screen on top, and using up the water relatively often, but the goldfish idea is intriguing.

Except that you can only get a permit if you get your water from a well, so it is illegal for the majority of us. That’s not to say I don’t have a couple of barrels already collected and gathering water…


Pretty much illegal in Colorado unless you live in an area that isn’t supported by a municipal water system… so illegal for a vast majority of the population of Colorado.

Colorado, where marijuana is legal, but collecting rainwater isn’t. (Not that either thing should be illegal, it’s just topsy turvy)

So hide it:

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