Eva888:  Does anyone have any idea of the amount of water that comes out of a unit?

Can't answer how much comes out, but even a small amount (if constant) adds up.

In our last house one of the water pipes under the laundry developed a slow leak - just a single drip every 5 seconds or so. Most of the dirt under the house was reasonably dry, but it was like a bog under the laundry because of the slow leak. Even after the pipe was fixed it took weeks and weeks for the ground to dry out.

In our new house there was a slight leak in the condensate pipe from our external gas water heater where they hadn't cemented the pipe adequately, so instead of going into a soak pit it just slowly dripped into the ground next to the slab (only when hot water was running). This was still enough for it to soak into the slab and have mildew start growing on it after only a few weeks. We found this quite early, so not major problem.

Moral of the story is even a tiny water ingress has the potential to become a big problem. Especially under the house where you can't see it.