Q. On question 3578 you wrote: “Using a single spout does not avoid the Bishul or cooking prohibition of the cold water being heated as it encounters the water emanating from the hot pipe that is Yad Soledes. It only cools down after being in contact with the cold water and having already transgressed on Bishul.”
Is that correct? Does not Halacha permit pouring a small amount of hot water into a cool water container, if the temperature of the cold water will not increase to Yad Soledes (About 45o)?
A. Horav Chanoch Ehrentreu Shlit’a indeed correctly questioned the above as is mentioned in Shulchan Aruch (O.H. 318: 12) that it is permitted to add small amounts of hot water that will nor rise the temperature of the container to a prohibited level.
However, one spout single taps, as explained on the next question, someone who wants cold water, usually and out of habit, turns on the faucet with the handle facing the middle and then pushes it over to the right or left to the desired temperature. In such a common case, the initial running water may indeed be over Yad Soledes at the beginning of the flow.
Besides, there are a number of taps that have built in pre-warming or cooling chambers and those may indeed create a bishul situation.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller, Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit’a