Actually, Hannys Papa covered it all pretty well, excepting that long-term the older parts of the shell (which the snail cannot renew) will erode in soft acid water. I have had MTS with white shell tips (rather than dark brown) in softer acid water as they reach full size, due to erosion.
But driftwood, unless massive quantities, does not soften water that much. In water which is moderately soft to soft you may be able to detech some decreases. In harder water, especially if you do good routine water changes, you may see some brown tinting of the water, but are unlikely to see much softening.