An apparatus with a thermal reservoir liquid that acclimates to room temperature in a building over time. A heat exchange conduit routes tap water through the reservoir liquid, cooling or warming the tap water on demand relative to water that is respectively heated or chilled in attic or exterior wall pipes by weather conditions. This provides a flow of water from a cold water tap that is tolerable for hand washing and is better for delicate clothes washing than either hot or frigid water from the supply pipes, and is done without powered refrigeration or heating. The thermal reservoir liquid is contained in a tub that can be made of a material with at least 10 or 1000 times lower thermal conductivity than that of the conduit, enabling fabrication of the container from plastic or other low-cost material.