Hi All
I have a need for a large underground water tank. the purpose is to store and then pump rain water and occasional pool water into the drain in the road.
my area is liable to flooding, so I have designed flood defences, including self powered pumps etc from a 2nd electricity source.
does anyone know where I can buy tanks suitable for underground. im in 34. ideally need 10,000 or 2 x 5,000.
thanks
local fosse supplier perhaps and/or SPANC. Other than that Gedimat or your local mairie could advise.
Weâre just investigating similar. There are quite a few types of suppliers like this
We had ours built from scratch by the builders who were restoring our cottage at the time. They just dug a huge hole and lined it with concrete and put on a concrete roof with a hole with a lid. Unfortunately we didnât realise we should have asked them to tank the concrete - one of those scenarios of not knowing the questions to ask - the next build will be easier. So the tank leaked for a few years and the horse chestnut tree nearby has never looked healthier. The leaking is much less these days so we think the concrete has tanked itself.
Not sure it cost very much. The builders were already on site with they tractopelle.
Funny seeing this, I have just returned from my daily dredging session of the wild pond, ready for my evening swim later, and, although the 2 ends are clear now (the only places my feet touch the bottom) the deeper central section is taking a lot of effort, so I was musing about pumping out, filtering at the same time and storing the water in a hired small (because of limited access) tanker. Then pumping the âcleanâ water back in again.
But I have just checked, the max amount of water in there is 42 cu. metres.
That is 42 tonnes. !!! Time to think again perhaps? Hmmm. 
Thanks for your repliesâŠmost helpful.
my French builders think im mad, but it would be madness not to have the system, and just let the whole place flood.
David, youll need a large tankâŠ45,000 litres min.
have you considered a pump filtration system, that pumps from the pool, out through sand filters and UV, and then back inâŠrunning all the time ? im not expert, but do often see them in my line of work; im an external lighting designer.
ill hit the internet and see what I find on the tanks. maybe ill upload some plans ive done for my builders. it might help others; and me !
before the comments startâŠI know ive spelt Jardin wrongâŠa quick typoâŠa faux pas
Had all that when I first dug it, Rob, very elaborate. There was an overlow at the highest corner leading down a narrow stream, underneath a boarded dining area into a smaller pond which in turn then overflowed down a mini waterfall into the bottom pond. This contained a pump powerful enough to send it all back up through hidden plastic pipes to fall back into the top pond.
Too expensive to run it all the time, plus the urinary stress of, (in particular ladies 
), to dine comfortably while hearing the tinkling flow underneath, I discontinued it after discovering that occasional use was ineffective.
I think Iâll just have to continue dredging, petit a petit. 
Hi David
thanks for the response.
there are some pumps that have a built in UVâŠso it can recirculate the water within the same pool, cleaning as it goes. yes, it needs to run all the time.
but sometimes that cost of electricity is far more preferable compared to the days and weeks to maintain manually.
your natural pool sounds wonderful. enjoy
Rob
At the moment I am gradually clearing the central bottom part and it is not too onerous, but the effort required to keep it clear will be more evident with the coming of autumn. Certainly at least twice daily clearing of surface leaves will be needed. Of course this would be needed anyway, UV filters do not repel leaves.
Interestingly the smaller, and much shallower, bottom pond that is much more in sunlight has perfectly clear water. Over the years green âweedsâ have increased in the bottom and I have resisted the temptation to clear them, just in case they are the reason for its clarity. 
They could well be, David. I donât have experience with very big ponds but the âoxygenatingâ things I had in the bottom certainly kept the water clear. However, nothing stopped the build-up of sediment or the growth of mats of azolla on the surface⊠grrrr⊠(People actually buy that stuff so it most have blown in from another pond!)
You have probably hit the nail on the head. If you looked at my link about natural pools (or just search diy natural pool) youâll see that the way they work is having a shallow area (only 30cm deep) of the same area as the pond planted with plants and they do all the filtering and cleaning. They recommend people also using the UV filter and a tinkling for the oygenation but I think most people put this on a little solar panel so no ongoing costs.
Interesting, both of you, it is very shallow the bottom pond, and the plants in some places reach the surface. If I could work out how to make a shallow area in the top, swimming pond I could transport some of the thicker growth perhaps. Does solar really need sunlight or just daylight? If not that could be a problem in amongst the trees.
Whatâs a tinkling? 
There are low energy pumps available, this is something I spent considerable miles and countless hours researching. Its what allows me to run pools so cheaply, and not without a nod to swim ponds as well.
Adding a speed controller should be high on anyones list and depending on the application the best filtration for the job.
For a pond or swim pond adding a drum filter should be high on the list as it will reduce the manual maintenance by a huge amount.
Have you power nearby or could you add it? Solar does need sunlight or youll need to quadruple the panels to be effective. That extra cost could dwarf the cost of putting in some power.
I bet your old pump was using close to 800 watts per hour? I have setup systems using less than a tenth of that.
i do have a power source close by but for the rest that sounds expensive. There are still the 2 pumps there as well as a large filter box, not sand, but not sure if they are still working or could be of use. I also still have the 2 UV filters I used before.
However, whatever I do to âpurifyâ the water, it still does not help with the massive influx of leaves at certain times of the year, which is my main concern, the amount of effort I have to put in to stop a build up on the bottom is considerable, and first I have to finish the dredging job, the result of several years of neglect.
Yes understood, you would need the addition of a skimmer of some type, plenty of pond types. That would help remove the leaves before they sink, the same applies to pools.
This is possibly the nicest natural swim pond I have seen in a long time.
