2001 ford explorer water leak

In general, coolant leaks can be deceiving in origin because of two things:

1 - It's mostly transparent so easy to visually miss; and 2 - It tends to leak when the system is hot and under pressure. When cold, even with the engine running, the system is only slightly above ambient pressure (there will be some pressure due to the pumping action of the water pump). When hot, pressure builds up to around 15 psi depending on the system to increase the boiling point of the coolant. Unfortunately, leaking coolant evaporates quickly on hot surfaces, making finding small leaks hard to find.

I would highly recommend getting a coolant testing kit from the parts store. I know the local Autozone loans them out for free and I'm sure other stores do also. It allows you to pressurize the system when the engine cold and not running so you can take your time and find leaks, and not worry about hot surfaces or getting shredded by the fan or belt. I had no fewer than 4 small coolant leaks on my vehicle (a V6 Explorer) at the heater hose connections due to bad clamps that I found using a tester.

Based on your description (and assuming you have one of the V6 engines) I would guess you have a thermostat housing leak, a heater hose leak, a water pump leak (either the seal or weep hole, either way the pump should be replaced), or a timing cover leak (if you are really unlucky).