Thunder Canyon has a reservoir at the bottom of the ride which contains enough water to operate the ride. In operation, the trough is filled by large pumps which draw the water from the reservoir up into the top of the trough at the top of the lift. When the pumps are shut off, because the whole course is downhill, the water all runs down the trough and ends up in the reservoir. Simple enough...
Water for the ride enters the reservoir from Sandusky Bay through a 12" culvert. I'm pretty certain, though, that both White Water Landing and Snake River Falls use treated, recirculated water.
--Dave Althoff, Jr.