In article ,
Michael Kilpatrick writes:
Three years ago when we had the extension built, I had also had a
rainwater harvester put under the ground in front of the house. It's
6.5m^3 and feeds the toilets, waters the garden and keeps the pond
topped. It takes 90% of the rainwater from the roof of the house.

If the harvester runs dry, I have an automatic system to top up the
toilet header tank with mains water.

The harvester has an overflow in the form of a u-band in the turret of
the tank which exits via 110mm drainage pipes into a 3-metre soakaway.
The level of the overflow is approx 70cm below ground level.

So, guess what? After over 2 years of lovely rain collection and
hassle-free use, what has happened? Well, it has rained *so* much this
year that the ground water table appears to have risen to approximately
70cm below ground level and has been sitting there for weeks. The
soakaway is therefore completely useless.

Which means that water is actually pumping back up from the soakaway
through the 110mm pipes, round the u-bend, and trickling slowly into the
tank at about 1 pint every minute. The water, of course, is now murky,
muddy and horrible!

This might have prevented something worse happening...
If the ground water rises a long way above the level in the tank,
there will be some considerable pressure trying to "float" the
tank, like a large bubble trying to rise to the top.
Does the construction of it have any protection against this
happening?

--
Andrew Gabriel
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