If that much stuff requires periodic washing maybe an alternate material like grating might be a better solution with a sloping pan beneath the treads to channel the water.
This is a typical detail for all transit stations in this particular line, and it is now installed all over Seattle....
Personally I think that if the mandatory 1.5" handrail gap and max 1.5" handrail are present, then the side "gutter is not a large issue for trip hazard due to the handrail compelling persons to be outboard from the wall. I do recommend to radius the nosing to side transition at the "gutter" so a foot does not hook if placed beyond the tread face.
Anyone else have input?