The June 2017 PM article by Anthony Tosco, “Heat up your bottom line with DHW recirculation,” claims it saves an average of 12,000 gallons per year. Philadelphia reports average total water use per household is about 54,000 gallons per year, and that includes exterior use such as landscaping and car washing. Many other water suppliers report similar total consumption. Of course, only some fraction of that is hot water.
To claim that hot water recirculation can save 12,000 gallons per household per year seems much too high, especially without any measured or metered data. Maybe one-quarter to one-third of the total water use is hot water, so hot water may amount to 13,000 to 18,000 gallons per year.