Just recycle an old water heater as the tank? I think your cost estimate is way overblown but it would certainly eat up a lot of time and effort to DIY. Regardl

Just recycle an old water heater as the tank? I think your cost estimate is way overblown but it would certainly eat up a lot of time and effort to DIY. Regardless there's a much bigger flaw with this plan. Water tanks need to be kept above or below certain temperatures. The "preheated" range being described here is distinctly unsafe due to various microorganisms IIUC.