no brakes

Can anyone tell me why my rear brakes only work when iI spray them with a hose?????????????? I go through rotors at (crossdrilled&slotted) 20000km intervals.THis has bin goin on for the last 5 years.I,m pretty muck done with this.I have yet to change rear drums,but had them turned and their within spec.How much of a role does this whole abs thing play into the water thing

I owned a 1990 dually that anytime it was wet the rear brakes would grab for the first application.The same could be said for my 98 Any thoughts :D