Dana, this isn't costing you by the word like a telegram...:)

How old is the house, where is the water coming in, where is it staying?

Most importantly, why in hell did you buy an old house only to tear it down?!!

You are in the wrong place if your plan is to tear down an old house--we own them and repair them because they have detail and charm AND VALUE which you cannot find in a new house!

Give us more background on yourself, the house, and what you want to do--otherwise you are just opening up a can of worms whose contents you really don't want to see.

Since the weight bearing of the old slab is not known, you are unlikely to be able to use it again (even under a new slab).

My neighbors just did this. They tore down an existing home and garage under 3000sf. I noticed they did make cuts and dig some new footings through some of the old foundation. Then they put the bracings for the new over 5000 sf foundation and indeed poured over. They only removed several smaller areas such as patios and the old garage floor, otherwise poured over existing. So, I believe it is possible. I was shocked they completely tore down the old. But they claimed the cost of the tear down was made up by the ease of building completely new rather then tying into the old. And all systems are brand new.