Tank for storing municipal water

Hi all,

OK… so I think the last big expenditure before I retire is going to be a tank to store municipal water to mitigate against outages in the municipal supply.

So the inlet side of the tank will be connected to the municipal supply (which is above ground at the point I will be placing the tank). The outlet side will feed whatever the municipal pipe feeds.

I would think I have to be fussy about the pump (or build a big tower and place the tank on that (but that sounds like a by-law infringement awaiting a penalty). This is because I have solar and people will do things with water after the sun has gone down. So I think that one of these vari-speed pumps (like you can get for a swimming pool to save on power) are a good option.

I would like to have an outlet before the tank, so that if I want to water the garden at night (when we are supposed to) the pump doesn’t run for 30 minutes or so and take a chunk out of the battery. This may present problems with the tank being depleted - or the pressure difference between the municipal supply and the tank may take care of things. IDK. I am even less of a plumber than I am an electrician.

Filtering: Well it’s municipal water which sits in reservoirs and in pipes (though it is probably always moving), but is it getting to degrade in the tank?

Also filtering: I presume that eventually there will be a build up of sediment. How does this get cleaned out? OK… filters to stop it going in (like my heatpump has). So regular cleaning of filters, which requires cut off valves on both sides of the strainer so that I don’t get water from the City or the tank all over the place.

I am thinking a 5kL tank. That’s 5000 kg when full if remember correctly from school. So sticking it up on the roof doesn’t seem like a smart idea.

I say 5kL because some months we come in under the 6kL free allowance that the City of Johannesburg grants for a month. So 5kL is going to get us a long way through a month (the garden will go to heck, but one can’t have everything). Even 2kL would get us through a week.

I suppose it’s possible to have a valve that will divert the city feed from the tank, to an outside tap. Which would sove the immediate problem, but is also one more thing that I may forget to remember.

Watching with interest for any ideas. I am planning to do the same thing. But I want to keep it as simple as possible. I already have 2 x 5000L tanks which collects rainwater. This is only used for garden watering and the fish pond. Also for toilet flushing when municipal supply is off, but still required filling buckets and carrying it inside. Higher one feeds the lower on with gravity and the latter having a pump. So I can get it into the house with a hosepipe if need be.

I would also want another 2500 / 5000L tank that keeps municipal water only but the trick is to get it into the municipal line and thus available to all taps which would be ideal.

Where this must/should happen I have no space for the tank and even if I had, then another pump is required as it is in the lowest part of my yard and the water needs to get up to a 2 storey house.

Was thinking to put a tank on my roof (concrete slab) but weight wise I think 2500L might be the limit (if even). From there I can gravity feed into the house for the backup gas geyser also via an emergency line (read hosepipe) and maybe even use a small inline 12V pump for a little bit of extra pressure.

So lots to consider still.

We did something similar (remember I’m in the same neighbourhood @Bobster with the same problems).

In our case we already had a 3.5kL tank that the previous owners installed for irrigation along with a pump. It gets filled up by municipal water which has a ball valve to shut off the inlet when the tank is full and the pump has a floating sensor to switch off when the tank is empty.

I got a plumber to just hook it up to the house through a pipe in an outbuilding next to the tank.

It is a bit tedious, but basically the following when I want to switch to the backup:

  • Ball valve to shut off the municipal supply
  • Ball valve to shut off the tank inlet (to not feed itself)
  • Ball valve to open supply to the house

And then the reverse once the water is back.

I could have done a split before the municipal shut off and use that as an inlet so that the tank can get water the moment the supply comes back, but that would have been a long run of pipe from the front to the back of the property, so I just rely on neighbours saying the water is back and then switch it back.

One thing I do remember was the plumber saying you must use a shut off valve (stop cock) for the municipal as they are safer than one way valves. I remember reading up on some forums and there’s two things to it in that you don’t want it to fail and then feed your municipal water that you bought back to the municipality and then have to buy it back and you also don’t want to potentially make neighbours sick should there be an issue with your water that you now fed to them and become liable.

In our case we don’t filter it (municipal as you said), but also don’t drink it when there’s an outage, but we use it for everything else.

The plumber suggested just cycling it every now and then which the irrigation takes care of, but when I need to fill up the pool I use the tank’s water to have an extra cycle of the water and as I’m not using municipal water though my meter I can do that before 6pm :wink: and just switch the inlet on again at 6pm.

At the end of the day although there are outages this works just fine for me instead of some fancy auto switch expensive thing.

If the outages are more frequent the thing you can maybe look at is a pressure tank. It basically keeps water pressurised, so if someone washes hands or flushes a toilet the pump won’t switch on until the pressure drops in that tank.

If you do go there, what I’ve learnt, get in contact with the engineer who designed/signed off the slab and ask them if it is allowed.

2500l is 2.5ton (as we all know) in a “concentrated” area.
Slabs are not normally designed for that far as I have been told by some engineers.
Spread over the slab, totally different story.

Ok so if I hook it up to any line in the house, then eventually the water should get to all the plumbing in the house if municipal supply is off provided there is enough pressure.

So if I do this on my roof, then water should gravity feed where it needs to be and I would get away with a smallish pump just for that extra oomph.

But then I should in this case (before opening the tank) shut off the municipal supply to keep the water from running back I suppose?

Ideally I would want the water to constantly circulate though. In other words as municipal supply come into the tank it must immediately upon demand service the whole house, and with a ball valve to shut off incoming supply when tank is full.

Yes this has me a little worried. The alternative but more cumbersome and expensive would be to rather use say 4 x 500L tanks, one in each corner of the slab where it is at its strongest.

But the plumbing involved to connect these together and have them fill up simultaneously etc puts me off a little.

I used 50mm pool pump pipe to connect 2 x 2500l rainwater tanks as one.

Connect the bottoms.

Sorted. Now have a 5kl tank.

… would still ask the engineer.

Yes that should do it, but the roof is a kind of a “braai room”. So the piping needs to look neat and out of the way as there is lots of corners and angles. Pool pump pipes are thus not an option.

If I remember, the rule of thumb for second story floors in normal residential homes is something like 600 to 800 kg per SQM, but I’m sure every engineer will have their own ways of doing it, it will probably also depend in what area the house is, plus when the house was built.

Rather than switching to the tank only when the municipal water is off, why not set it up so you permanently use water via the tank? This will also sort keeping the water fresh for use.

Municipal feed, ball valve, filter, then another ball valve, then in to the tank. The type of filter/s you want to use will depend where you live and on the quality of your water.

Rather than a separate branch/tap from the tank outlet which you can use for watering the garden without the pump running, I would just place the pump on a smart switch which you can switch off when you don’t want it to run. Note however when some pumps are off, it actually restricts the water flow, so this won’t work with all pumps.

Expensive VSD pumps is the way to go, however here on the farm I use normal cheap and chearful centrifugal pumps, when the electricity is off they also don’t restrict the water flow at all.

When placing a 5 kl tank on the ground, you don’t have to even throw a extensive slab, as long as it’s well compacted level soil you’ll be good, if you want you can also place it on a base of large pavers or smaller paving bricks. As long as it’s level and the entire base is fully supported.

Was what I was thinking. If I’m turning the water over all the time, then it should stay reasonably fresh.

After work on the pipes we do get sand/mud in the water. I assume this settles at the bottom of the tank and so must need cleaning out eventually.

Thanks for all the useful information.

At the inlet you put a disk filter for mud/sand/bigger particles. On the farm I have a disk filter which I take out and wash around once a month if I remember.
Just go to your closest irrigation place and tell them what filter you want and they should be able to make something up for you.

As for cleaning the tanks I haven’t done mine in 2 years, it’s actually pretty easy especially if your tank is on the ground. Disconnect everything, tip the tank on its side and wash it out with a hose pipe or high pressure washer.

Maybe I should also just add, a typical Jojo tank have a big 480mm lid on top, which makes it easy to hose out.

We have had a lot of outages over the years, the worst was a house full of people for a whole weekend.
Last year I decided to do the installation, after seeing quotes from others and the work they do, I decided to DIY it. I spent some time finding “specials” all in I ended up +/- 10K. 2050L ECO Tank with Pascali 0.75 pump. My mainline was easy to tap into before it goes into the house. I didn’t build a pad for the tank, I will look into it if I pick up issues.




With the flooding in KZN last year or the year before, family of mine’s water was cut off for weeks.

The plan they made was to pump water out the swimming pool in to their tank to feed the toilets and geysers, they assured me a shower using pool water is 100x better than no shower at all.