Can you help with this inquiry about WHO wastewater standards?

Can you help with this inquiry we received?
"I am working on a project in the Caribbean, and was told us that they use WHO norms for their water treatment. We are working on a waste water treatment project, so we starting looking ourselves on various websites that deal with the WHO and waste water treatment. Needless to say, we found plenty on potable water treatment, but nothing on waste water treatment. Might you know of, or where I could find some guidelines, or if they exist?"
We suggested the Regional Office for the Americas of WHO in Washington, D.C. but they haven't received a reply yet. If there's a web link please post here?