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 120^oF (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 cold water are controlled by one handle.  Generally, it works as follows:  When turning on the faucet with the handle set in the middle position, there will be an even mixture of hot and cold water.  As the handle is turned towards the right, a valve closes off the hot water and the water will be mostly cold; if the handle is pushed all the way toward the right, the water will be only cold.  In this case, to avoid Shabbos transgressions, one would use the one-handled faucet with the handle turned towards the most far-right position.²

Nevertheless, this handle poses a Shabbos challenge since one always has to remember to first push the handle lever towards the far right before turning on the faucet.  This is not how it is normally done. Typically, someone who wants cold water turns the faucet on with the handle facing the middle and then pushes it over to the right.  Force of habit might cause one to do this on Shabbos.  Also, a guest or child might not realize that this is an issue at all, and may unwittingly transgress the isur of bishul on Shabbos.³ An additional concern is that some one-handled faucets do not turn “all the way to the right.” They can be swiveled to turn 360° all the around.  A person can easily misjudge the acceptable position of the handle.

There are some one-handled faucets which have another problem, since by design they never shut the hot water off completely.  This means that even when the handle is turned completely towards the right, some hot water still comes out. This can be tested by turning the cold water shutoff valve underneath the sink, then turning on the faucet with the handle positioned towards the right. If water continues to trickle through, then the hot water is still coming out.⁴ Therefore, even if one is careful to position the handle all the way towards the right before turning on the faucet, one may still be using some hot water.

Practical Recommendations:

1. Turn the hot water shutoff valve underneath the sink to the “off” position every Erev Shabbos.⁵ This could also be done on Shabbos, as there is no melacha involved.
2. Install a two-handled faucet to avoid the problem.

Turning the water heater ignition to the ‘pilot’ position does not solve the problem. Even though the heater will not turn on, the water entering the tank will still be heated upon mixing with the hot water in the tank.

If you are at another person’s home on Shabbos, can you use the one-handled faucet? Are you required to ask the host what he has done to resolve the problem? Rav Moshe Heinemann shlit”a rules that this is considered a sha’as hadchak, a pressing need, since a guest may be uncomfortable asking about handles. Based on halachic principles referenced in the footnote, one may turn on the faucet with the handle positioned towards the right.⁶ However, in one’s own home, this must be rectified before using the faucet.

What should you do if you turned on the faucet with the handle positioned towards the middle and realized you made a mistake? Can you turn it off?  In a typical case, when you realize it right away, you may turn it off.  The water that has already come into the tank is already hot, and you are merely preventing more cold water from being heated.⁷

On Yom Tov, cooking is permitted and one-handled faucets may be used.  You may also use hot water for permitted uses, such as washing your hands.  This assumes you are using a conventional hot water heater, which incorporates a tank. Tankless systems cannot be used on Yom Tov, and certainly not on Shabbos.⁸

Modern conveniences, such as flowing water, have added immeasurably to our enjoyment and oneg Shabbos.  With some forethought and care, we can ensure the acceptable use of these amenities.