Now imagine a chain of canals, etc... using gravity and the slope of the earth to send water to where it's needed.

Because of the plumbing being in the floor creating the gravity issue an above ground sump pump unit won't work. 

The chimney probably needs looked at because there was a dead chipmunk in there.It has an old gravity furnace, and old normal furnace.

Is the water mitigation a interior sump with drain tile, cutting out concrete, patching in to match existing, or is it via sump with exterior gravity drain tile.

Gravity is a cool project down there, but I'm gonna hold off for now.

The water is on a well and the waste is gravity fed to a large bank of septic tanks that are periodically pumped. 

This is the long way around to say that if you are using money from a refi to make your next move it has a bit more gravity then if you pulled the down payment out of your bank roll.  

Bathroom walls unsupported from underneath so they could run plumbing, gravity fed heat ducts which all had to be removed and replaced with more modern heat.

The latter can sometimes compromise the expansion tanks as well.One deciding factor for me was the CO intrusion issue with back drafting on the old gravity vented units & we have had several in the past trigger the required CO alarms.

the risk with california is not the law but the gravity of price moves.