Here in the Spokane-CdA area, we're fortunate to have the Rathdrum Prairie Aquifer, recognized even a century or so ago to be one of the planet's cleanest and most productive sources of ground water. But yeah, everything from BNSF's refueling facility to the corner gas station and all those subdivisions getting planted above the aquifer are something to think about. Even during drought years, by the time the snowpack has dwindled and minor streams are drying up, the large lakes surrounding the aquifer keep it reasonably well fed. The head of the aquifer is Lake Pend Oreille, and that huge body is fed by numerous sources, not the least of which the Clark Fork River.