I have always liked this idea. A glass-lined water heater is probably as inert as you'll get and you can store a lot of water and keep it fresh. However, one concern I have with such an arrangement (and I meant to comment on the other water thread in LTP where such an inline storage option was mentioned) is isolating the water in case something happens to the quality of the incoming water supply. Could be a widespread failure like the Milwaukee crypto incident, or just a localized one like a sinkhole down the street causing sewage to contaminate the water main leading to your house. By the time anyone is aware of the problem, your tanks might already be contaminated with bacteria or chemicals that shouldn't be in there.