Bear in mind that we tested the water coming out of the sewage pipe, not the river water. There is a lot of info available, and can be quite confusing:
This is a NRW report – https://naturalresourceswales.gov.uk/about-us/news/news/tighter-phosphate-targets-change-our-view-of-the-state-of-welsh-rivers/?lang=en
UK Government guidance recommends that rivers should not exceed annual mean phosphate concentrations of 0.1mg per litre. https://view.officeapps.live.com/op/view.aspx?src=https%3A%2F%2Fassets.publishing.service.gov.uk%2Fgovernment%2Fuploads%2Fsystem%2Fuploads%2Fattachment_data%2Ffile%2F1126652%2FPhosphorus-challenges-for-the-water-environment.odt&wdOrigin=BROWSELINK
The UK drinking water standard requires the nitrate concentration to be less than 50 parts per million. https://thewaterprofessor.com/blogs/articles/nitrate-in-drinking-water#:~:text=The%20UK%20drinking%20water%20standard%20requires%20the%20nitrate,common%20problem%20for%20private%20water%20supplies%20%28water%20wells%29. NRW has much ino too: https://naturalresources.wales/about-us/what-we-do/water/nitrate-vulnerable-zones/?lang=en
In the US recommendations officially state the limit for nitrates at 10 mg/L. Nitrates in Water? Safe Levels and How to Remove it – Pick: Comfort
Hope that helps
