I have faced a problem with rust in water supply system: there was production downtime and no water was consumed for several days, when production started we found some rust in water and therefore we were forced to rinse it for several hours.
In order to protect the customer form rust particles accidentally appear in water we are going to install some sifters. The question is what is the mesh size needed to be used (as HACCP approach requires to set it scientifically based)? There is requirement concerning turbidity only in local legislation, but nothing about particles maximum size. Similar situation in WHO web site - there are some requirements concerning chemical and microbiological aspects only.
The question is rather close to foreign body maximum size that can be consumed by a human without harm, but still maybe someone faced the same situation choosing water sifters and can tell how he/she has done.