How about some sort of Venturi measurement system?
Utilizing the water's electrical conductivity abilities to shortcut an electronic circuit when the water floods the measurment hose because of lowered flow rate and therefore higher pressure. Instead of using the water to shortcut the circuit a "floating metal ball" of some sort could do the trick
It's certainly cheap and safe, and give us both flowrate and safety. But on the other hand cumbersome and demands testing and thinking.