Build Solar Water Heater

i have a solar water heater in my residence i want to know wheather it is safe to drink that water if we take preacaution while storing and collection from the solar water heater/

I want to build a batch heater or a passive coil system on a painted black corrugated metal backing. But I want to be able to stop the flow when the water gets to a set temp. It would be great to be able to just put in a car radiator thermostat but it would allow the water to get too hot.

i am constructing a solar water heater now as one of the requisites in our curriculum and I’m wondering what is the cheapest way of constructing it?

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