Use hot water tap on Shabbos

If I live in an apartment building that has lots of non-jewish tenants, can I turn on the hot water faucet on Shabbos?

Not allowed

Why is this not allowed?

Because you will be heating up water on Shabbat which is prohibited. The fact that there are non-Jews in the same building doesn’t change anything.

If the building is large enough would it cause a scenario where there is a safek who is triggering the boiler to refill?

No, does not help.

what if the building has a solar water heater?

Can you clarify if you are saying it is not considered a safek or it is a safek but safek (derabonon) doesn’t help?

Turning on the hot water tap on Shabbat is prohibited even in a large apartment building where non-Jews also live. It is prohibited.

What is a solar water heater? The water is heated in the sun or the hot water system is powered by the sun?

Are we just asking theoretical questions?

Not theoretical. More and more places are switching to using solar energy for water heating. For example, in my house, we have panels on the roof that the water lines run through. When the sun shines, the water is heated and then circulated to my insulated water tank that holds 110 gallons of water. No outside power is needed. Some apartment buildings and resorts use this technology also (Disney’s Bonnet Creek resort in at least one of their buildings does this).

In some cases, like mine, the sun is directly heating the water. In others, solar panels will provide electricity to the house which will then operate an electric water heater.

So, my two questions would be 1) if the sun is directly heating the water, do you think it’s OK? and 2) is it ok if solar energy panels are gathering energy from the sun and then converting to electricity to run the water heater?

Does the insulated tank heat it at all or it just keeps it hot, but loses heat as time goes, like any thermos

Insulated tank does NOT heat it at all

The water heated by the sun is ok. They use these in Israel on Shabbos also.

Thank you.

Why is it not considered in a apartment building פסיק רישיה שלא ניחא ליה because the heater getting warmed up will be used by someone else or at least a ספק פסיק רישיה which many hold is permitted???

I believe one of the issues is that you actually want the new water to enter the heater because that is the pressure that allows the water get to your faucet. @ytesler am I correct?

From what I understand, in large apartment buildings (i.e. 30+ floors) the boiler would not need to be refilled in order to supply pressure to allow water to come out of the faucet. In other words, if the pipe allowing water in to the heater was shut off, I would still receive enough hot water for a shower. Assuming this is true, would it be permissable to use hot water in a high rise building on Shabbat.

It really depends on how it works. You are asking a general question and making very specific assumptions that make a difference whether or not you are being mechalel Shabbat. Please verify the details and then ask with all details in place. Thanks.

If you are able to set your water heater to be under yad soledet bo, can you then use a hot water tap on shabbat? I believe many water heaters can be set to be 120 degrees.