It matters because bodies float to the surface, however water washes away anything that can be forensically matched to the killer, but its still more beneficial to dispose in the deepest water possible.. there are certain lakes, so deep its impossible to recover a body even if they suspect a body was thrown in btw... true story that.
You haven't thought this through mate, especially if their DNA is all over your gaff, unless you make them climb in to a bin liner before stepping over the threshold.

