Many independent and government agencies provide access to detailed information and reports on issues related to clean water. Below is a list to get you started:
You can use Google to easily search government websites by including site:.gov at the end of your search string.
Another option to try is site:.int, which will search international sites (e.g. World Health Organization).
Because most reports are published as PDF files, you can also limit your search to a specific filetype by adding filetype:pdf at the end of your search string.
Sample search: clean water site:.gov filetype:pdf