The Kodak Hypo test kit gives a standard reference in color and in quantity of retained hypo and silver halide in a coating for archival wash. Early Kodak manuals give in the range of 1 hour washing in running water to achieve this level for film and some FB papers.
I won't suggest that this is needed for modern papers or films, but I know this, that single wash baths are not efficient. Here is the reason:
Wash 1 can only remove 1/2 of the chemicals from the coating. This is a law of science shown by Mason.
Wash 2 can only remove 1/2 of the remainder using the same math.
Wash 3 can only remove 1/2 of #2.
And etc. You approach zero but never get there because the wash water you use never has zero chemistry in it. It always equillibrates with what was in the film from the past condition.
Now consider running water. It is always zero in chemistry and as it passes over the film, the exchange is roughly double that in single baths and it can get to zero in the film (or a very very tiny amount).
This latter wash can be quicker and more economical when done properly, but you must not overdo the wash.
Simon is right though. Today we must conserve our resources and this is why Ilford and Kodak both came up with the other method in hopes that it would conserve water, but misused it can result in underwashed photo materials. So, I suggest that in the final analysis, you use the silver halide retention test for rate of fixing, and the hypo retention test for rate of washing whatever method you choose for washing your film and prints.
And, don't chance it to water from rain or from dehumidifiers. Both of these contain atmospheric contaminants and bacteria that are not present in distilled or tap water.