Wolseley, in conjunction with the Canadian Mortgage and Housing Corporation have provided a "Sustainable Plumbing Checklist". On that list under Bathroom Checklist, you will find "Drain water heat recovery" as one of items that is recommended.
"Water heating is the first or second largest residential energy use, accounting for 15 to 30 per cent of total consumption (IAPMO 2012). Hot water systems are composed of the heater, the distribution system, fixtures and the drainage system. Energy efficiencies can be found along each step of the way." (source: CHMC "A GUIDE TO SUSTAINABLE PLUMBING IN THE HOME").
"During and after use, heated water that contains energy goes down the drain. Drain water heat recovery devices use the warm wastewater to preheat the incoming supply of water and thereby reduce the amount of energy required to raise the temperature to a set level. The cool incoming water passes through a series of coils wrapped around the drain stack and heat is transferred through the copper walls of the heat recovery fitting. Although they can be installed on any vertical drain, they are typically found on pipes serving showers. These devices could recover 40 to 75 per cent of drain water heat, depending on the shower flow rate, plumbing system and type of fitting installed (World Plumbing Review 2008)." (source: CHMC "A GUIDE TO SUSTAINABLE PLUMBING IN THE HOME"). https://www.kitchenandbathclassics.com/wp-content/uploads/Guide-Sustainable-Plumbing-CMHC.pdf
This clearly indicates that both the plumbing distribution channels and the government have both adopted the recommendation to install drain water heat recovery technology as part of a sustainable plumbing system in your home.