system
Given the following post, respond as if you're commenting on Reddit:
human
Is it more efficient to boil cold tap water or to wait for hot water to start running out of the tap and then boil that?

So I imagine the two competitors here are the efficiency of my gas stove vs. the efficiency of my hot water boiler? Maybe they're not that different (both run on gas) - if so, is there a cost difference?

If they're the same, the obvious loss of efficiency comes from the cold water I waste while waiting for hot water to run - right?

***TL;DR: Thanks for the responses! It seems almost unanimous that drinking hot tap water is a health risk for a couple good reasons, although it will be faster to boil. But in regards to the original question, I agree with many others now that a real dive into the energy use and water waste numbers would be difficult and time consuming. Boil cold water, yes?***
gpt
Regardless of efficiency, it is safer to take cold water and boil it. Hot water allows for more things to be dissolved in it, and depending on your pipes, you could be increasing intake of unwanted substances.