"On the 2005 Discovery / Excursion it's very easy to get to..."
it depends on the model, my 2005 model 35 Discovery has the water pump hidden in a cubby hole above & behind the rats nest of hoses & wires in the water service bay. You can't see it or touch it without completely dis-assembling the entire water bay. there was no access from above planned into the layout. I've cussed that engineer for 10 yrs. Fleetwood had no suggestions, they denied the WP was actually located there, since they assume its the same as the 39 model layout.
I had to cut a hole in the side wall from the adjoining storage compartment to get at it.