While I don't have a pond(and likely won't, as I don't use water stones really), I have been thinking through a system that would provide water drainage into a bin and use one of those air compressor powered venturi coolant sprayers for some of my bigger, powered grinding projects. I've idly wondered if I could slow down the feed rate and allow myself to have a slow drip water source above and a place for it to go under my stones, avoiding the mud problem mentioned earlier, and giving some of the cleaning benefit that a pond might.