Winter 2012

Torah-observant Jews know that turning on the hot water faucet during Shabbos causes cold water to be heated, which transgresses the melacha of bishul, cooking. What many don’t know is that even turning on what you think is cold water can be a problem – if it’s a one-handled faucet.

Let’s first analyze why using hot water causes cold water to be heated.  In a typical home setting, cold water arrives from the city supply under pressure.  Turning on the hot water faucet allows this cold water into the hot water tank which, in turn, forces out the hot water already in the tank.  Since the water in the tank is typically more than 120oF (the minimum temperature for bishul on Shabbos), the incoming cold water is immediately heated by the hot water that is already in the tank. 1

In a one-handled faucet, both hot and […]