Question:
How many
gallons of fresh water per person-hour of use, to avoid using any
chemicals?
Answer:
if the tube in the tub leaked (it
carries water from the water heater), at the same time as a water supply
failure, then tub water could be siphoned into the house water supply and
therefore, the city water. Obviously, a leak in my current in-the-tub heat
exchanger would result in quickly detected overflow of the tub, so the
simultaneous failures are unlikely. But that apparently doesn't meet code.
I did some research at the library today. The wording in the code doesn't
make it clear whether my counterflow heat exchanger idea might work. A
double wall heat exchanger clearly would. Tomorrow, I'll research where I
can actually get one, and what the cost might be
