Welcome to Defra Data Services Forum

Within the WQA Explore option you can search under sample point type: 

https://environment.data.gov.uk/water-quality/view/explore

This looks at the sample level rather than the determinand and is ok for environmental monitoring but not for other types of sample point type used for compliance.

In the download section you can look at the determinand level by filtering on the sample material type in column M: 

https://environment.data.gov.uk/water-quality/view/download/new