A water-tempering apparatus reduces water temperature, to prevent overly-hot water from flowing into a drain. One disclosed apparatus includes a drain water tempering assembly that fits into the collection pan of a trough floor drain. The apparatus includes a valve, a cold water line connected to the valve, and a temperature control for causing the valve to open and dump controlled amounts of water into the over-heated water in order to cool the heated water to or below a legal-maximum predetermined temperature. A related apparatus includes portable tub with wheels and with temperature control components. A related method is also disclosed and claimed. The assemblies can be shaped for retrofit installation into an existing commercial drain, or can be for new installations, or can be a portable unit. The apparatus preferably uses non-electrical thermostat-operated control on a cold-water-supply valve.