There are many kinds of bathroom faucets, and you may have both single and double faucets in your house, if you own an older home. But most newer faucets are singular, and this sometimes confuses people who do not understand why this is necessary, especially if they are asked by an official buidling inspector or real estate inspector to change out the dual type of faucets and replace them with single ones, which can and usually does require also changing out the whole sink apparatus. If you have these for example in your kitchen or bathroom, built into the counter or vanity or other furniture that is part of the permanent fixtures of the room, the act of simply changing faucets to comply as single faucets can in some cases mean you have to rip out all of that stuff and start over, because the sink is frequently an intregal part of the built in fixtures of a room.
The reason that many of the older type bathroom faucets that offer water out of one faucet that is cold and hot water out of another one are frowned upon by inspectors is unknown to many people who think this regulation is irrational and unreasonable, with no basis in common sense. But the reason that some ordiances call for a single source of water controlled by both hot and cold valves or taps, is because in the past there have been safety issues with having a single hot water faucet, because people turned it on and their hands were scalded by the water. Another issue is that with both, the user is not able to mix hot and cold, to get a hot temperature that is tolerable but hot enough to be sanitary.
So it is preferred to have two taps that control both hot and cold water than flows out of a singular central faucet, where the water can be mixed by adjusting the flow of hot and cold, until the temperature is ideal for the user. These kinds of bathroom faucets are found in all home improvement stores and modern sinks are all made to function nicely with this type of faucet.
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