How to use an existing concrete reservoir?

On our land when we arrived was a concrete reservoir. Concrete wouldn't be our choice for a pond, but it's there, and it feels pretty wasteful and time consuming to dig out the concrete and throw it away. It did not hold water up to now but if it did, it would hold about 35,000L. i attach a picture. We're currently sealing it as we're heading into rainy season, and would like to start to make use of it but we're not quite sure.

(background: We have a Mediterranean climate, about 900mm of rain, almost all of it in winter (no frost, lots of wind, horribly hot, windy summer).)

I would love advice on how to use the reservoir best. We have very very limited electricity-- solar, not enough for a pump-- so the challenge may be keeping the reservoir non-smelly/non-deadly to water creatures.

Our ideal would be to use rocks already on the property to make a gradient of shallow and deep portions, add a variety of water plants (including floating plants and reeds), and tilapia who are not fed, but feed on the plants and on the duck poop (we have 6 muscovies). Is this a realistic vision? We wouldn't want a huge number of fish, but I'm really not sure of the proportions to think through. What I've read online usually refers to ponds with natural (clay) bottoms, or with pumps/filters. Our plan if we had a lot of algae was just to skim it off and add it to our compost pile. So not a very complex plan...

If anyone has experiences and/or advice to share, I'd be super grateful!

What a great asset!

My largest homemade pond is round, 3 feet deep and 16 feet across (diameter). I have a few each of tilapia, koi, goldfish, plus many guppies. For pond plants I have azolla, water hyacinth, and pennywort. About 1/2 of the pond is heavily shaded. Once I created it, it took about six months for the pond to balance out, but it eventually became clear and lovely even without a pump.

Then I acquired two Muscovy ducks. And it didn't take long for them to muck it up. Within a few months the pond became a dark, mucky, cloudy, smelling cesspool. Last month I finally confined the ducks....no more pond access. After scooping the major portion of the built up sludge from the bottom (tilled into the garden), the pond is slowly clearing up. I can see the fish now when they near the surface. The stink is gone. I expect it will take another month or two for nature to repair the damage that the ducks did. Obviously, my pond is way too small to survive the impact from two ducks.

Thank you so much Su -- I am a big fan of your blog and really appreciate your taking the time to reply. I'll think of other swimming options for the ducks!!

Muscovies apparently get along fine without a pond. Lots of people in my area have them with no ponds and just supply a water bucket for them for bill cleaning. I notice that the ducks really want to dip their bills while and after eating.

I like to give my ducks a mini pond to float in just because they seem to enjoy it. So I use one of those big black concrete mixing tubs that I bought at a building supply store. It's big enough for them to float and preen, and small enough for me to be able to dump it over twice a week in order to refill it with clean water. I tried using a kiddie pool but it was too difficult to dump. It didn't take long before it cracked.

Thank you for enjoying my blog. It's far easier for me to blog than answer zillions of emails. Plus I find that it's a fun thing to do in the evenings. Now that I'm trying to have the homestead earn an income, I'm finding that I have less time on my hands for blogging. Hopefully once I get a system set up and functional, I'll find myself with free time again. If you any subject you'd like me to blog about, feel free to make a suggestion. I've been able to devise some neat experiments based upon readers suggestions.

Thanks Su. We've (ok, my husband, but it's still "we" because I was with the 3 kids) sealed the pond and are waiting for rain. The main thing I like about your blog is that it's down-to-earth and shows a lot of flexibility in approach. We're just 1 year into living on a much smaller homestead than you, but so far it's apparent that being flexible is key, and acknowledging when something is not working (and sometimes waiting for a while if that's possible, to see if it's just not working yet).

Thank you for the compliment, Jo. "Flexible" is a good word to describe my approach. When things don't work out, I'm always willing to backtrack and try a different angle. Or take a failure and work it into something else.

My goal has been to create a workable homestead for ourselves, using a low tech, low input approach. Along the way I've learned about organics, natural farming, permaculture, bio intensive, and many other techniques. How fun to see what other people have discovered and created! My biggest discovery has been "what works for one does not necessarily work for another". Perhaps my flexibility trait stems from that.

There's an old concrete reservoir on my parents land that we've put back into service a couple years ago. Maybe half the volume of yours. It was more-or-less watertight all these years, we just left the drain open as we had ample water in the pond. Since we've had droughts the last couple summers we wanted to use this as well, just in case.

There is no effort made to oxygenate or circulate the water, but it has become ridiculously full of various life, and the water stays clear, barring a couple cloudy weeks in the spring when something blooms and then whatever eats it catches up.

Ducks visit occasionally, but don't stay long. We haven't stocked it with fish as we cannot be sure it will have water through the whole summer if things continue as they have, but it is home to a vast array of water insects, including dragonfly nymphs, and thousands of tadpoles. We were inundated with baby tree-frogs. The big frogs which inhabit the main pond only 30ft away haven't moved in, which has made this place a sanctuary for the little tree-frogs.


The only issue we've encountered was a sad one; the reservoir is within the deer-fenced garden area, but our repairs and salvaged fending were inadequate and a doe broke through the fence and presumably traversed the reservoir to access the garden beyond it. Her two fawns followed her, and couldn't get back out of the reservoir, or touch bottom; we found them drowned. Removal of the bodies was not a pleasant task. We now have better fencing around the area; definitely worth thinking about, especially for those with livestock or children to worry about.


I'm with Su Ba as far as the ducks go; your pond isn't big enough to absorb the amazing amount of muck they create, and remain generally pleasant. It could still be done, with the thought that the mucky water would be excellent for irrigating things with, but it would preclude other possible uses in my opinion.

We just use ours as the water source for anything we are watering by hand; last year that and evaporation used about 60% of its capacity by the time the rains came. In an emergency (if the reservoir-pond runs dry) we could rig up a way to feed the main watering system from it, but it wouldn't last us very long. We'd need to replenish it from the well(if that wasn't also dry)...

Thanks very much Dillon. Very helpful. We've had our first rains and have started to fill the reservoir from our rainwater tank (it took about 24 hours for our 5000L rainwater tank to empty into the reservoir!

I had this (foolish) idea to make a living fence, and planted about 50 kei apple and Natal plum around the reservoir. It may work eventually, but for now we have to be vigilant with our children, as the living fence grows very slowly.

We'll keep the ducks out-- may still need to figure out exactly how best to do that. So much of planning so far has revolved around fencing!

Thanks again for taking the time to respond.