We are currently conducting research involving tests for high level phosphates, but have yet to find tests that we’re happy with. Field tests that are currently available on the market can you let you know if phosphates are present, but can’t tell you to what extent they are present. In other words, they’re not quite sensitive enough to be useful! Also, many of the field tests require you to handle reagents that can be toxic, and that makes disposal difficult, meaning they wouldn’t be safe for kids to use. We are watching this space closely, and working with partners to see if this can change.
While we have seen some field tests that give you an ‘absence/presence’ for E. coli, they are bulky and expensive, and often single use. They also don’t give us a numerical value, making them irrelevant for natural water systems (where a count of 200 would still be safe for swimming). Absence/presence would give too many false alarms. All of this to say- you need a lab to test for E. coli!