Upvote:1
There does seem to be a product category for exactly this.
For example
https://www.simplexhealth.co.uk/product/aquarium-fresh-water-5-in-1-50-strips/
https://www.simplexhealth.co.uk/how-to-test-the-quality-of-open-water-for-bathing-or-swimmingis/
Notice the section,
"Recommended Tests for Open Water Swimming:" / then / "field test kits which provide instant results (these are suitable for fresh water only and are screening tests)" ...