Having just read through the RA guidlines(20-01-12) I found a section that states that water samples for microbiology testing should be taken from the flow and return, a mid point AND a point furthest away from the incoming loop side.
As one of the authors I have to admit that this paragraph is not that clear. If I am involved in the revision I'll try to remember to get better clarity. I think to a certain extent the sampling points depend on the design of the system; so when it states one sampling point should be the furthest point in the distribution loop and another should be on the return point, in most modern systems without a RO water holding tank these two point sare the same. Does that help?