Drainage pits - how many?

I'm interested in knowing how many drainage pits people have in their new homes.

These pits are 450 x 450 wide with a grate on top of them. They're an eyesore and probably expensive, so the fewer the better.

So please, let me know how many of these pits you have in your new home, even if it's zero.

If anyone has knowledge in this area, I'm interested in hearing what their purpose is.

HI Casa

Ours have not been installed yet however we have just moved into a rental that is a brand new house. It has what we are expecting at our block, small black plastic ones about 20cmx20cm. The number of these required will depend on the fall of the block I think. At the rental there is about 6, at the house we are building we are only expecting 2 as water at the back of the house will naturally fall to the canal. So they have placed one either side of the house towards the front.

Where they were put and how many there was depended on the land survey that was done with our soil test.

Anne