In Israel, when outside temperatures are high, the water from the cold faucet becomes very warm. Is there a problem washing hands or food etc when this will cause the water coming into the faucet to be heated.

Shalom, Thank you for your question. Water that sits in the pipes leading to the house can certainly become hot in the Israeli sun during summer. This is not a problem at all on Shabbat. Let’s examine the laws of cooking with the sun on Shabbat. The Torah forbids cooking on Shabbat. This includes cooking on a fire (of any type, including electric). Not only that, but cooking on a utensil that itself was heated on a fire is also forbidden. So heating up a frying pan on a fire, then cooking an egg in the pan, even away from the fire is forbidden. However, cooking in the sun is permitted. So one may put an egg out in the sun to cook. So too, water that is heated in the sun is permitted on Shabbat. The Rabbis made a restrictive law which forbids cooking on utensils that were heated up in the sun. If one puts a frying pan out in the sun, then cooks an egg in the frying pan, it is forbidden. The reason being that one may come to use a frying pan heated up on a fire (which we already explained is totally forbidden). The only problem one could imagine with your question is whether the pipes themselves get hot enough to “cook” the water in them. If so, maybe we would consider that as a case where the water is not heated by the sun itself (and permitted), but heated by a utensil that was heated by the sun, and forbidden (like the frying pan case). But, in truth, it is not comparable for several reasons. Firstly, it is doubtful that the pipe itself gets hot enough to heat the water by itself – it still needs the sun to really heat up the water, and as such it is considered as water heated by the sun, and not by the piping. Next, because we are talking about the cold water tap, you do not want the water to get hot – so we lack intent, making the law more lenient. Thirdly, the water will not definitely reach the level of heat that is considered “cooking” (this will depend on how long it sits in the pipe, the weather, and other factors. As such we do not have a definite situation, which is also a lenient factor. In summary – you may open and close the cold water tap even if the water that runs through the pipe may reach a hot temperature due to the sun shining on them. In Israel most houses have a solar power hot water system – but the use of that on Shabbat can wait for a different question and answer. Blessings.