Dear Umbra,

You know how, when you turn on the hot water in an old building, it usually takes a while for it to kick in? Well, my question is, if I turn on the tap full blast, will the hot water come sooner? Is it the amount of water you let run, or the amount of time you leave the tap running? I’ve talked to my landlord, but in the meantime, can I save water by letting it run slowly?

(No) Hot (water) and bothered

Dearest Silly Pun,

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You know I love to share my water-heater knowledge.

There is a water heater in your building, connected to your faucets by yards and yards of pipe. The heater, most likely a tank-style heater, keeps its electric elements or gas burner busy throughout the long days and nights. The water in the heater is hot 24/7, and ready to rush through the floors and walls to your faucet. After you use hot water and turn off the faucet, the eager water is stopped short and left to wait in the pipes until it is once again called into duty. As the water stands and waits, its heat is eventually lost to the pipes and their surrounding air. When you once again turn on the faucet, the first water to pour out is that which was once hot and has now become cold. So you need to run it until you’ve bypassed the stale water, and fresh hot water has once again reached your apartment from the bowels of the building.

That is why it takes a while. Pipes are always filled with water, and operate on that system we might have learned about in physics class — a sort of pressure system where you are basically drawing up the new hot water by releasing the ex-hot water. As you may see, there probably isn’t much your landlord can do to shorten your wait. Pipe insulating tubes might help, as they delay heat loss, but the amount of exposed pipe available to an insulator is likely quite wee.

I don’t think you can do anything to change the amount of water wasted in any given hot-water demand moment, whether you run it fast or slow. Just run it till it’s hot — and if you are super-industrious, collect it in a bucket and use it for something. Watering plants, or dousing attacking Mongol hordes.

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