system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When I boil water, why am i supposed to use cold water?

Wouldn't warm or hot water just speed up the process?
gpt
This originated in countries with municipal hot water that was run through metal piping. The hot water is a lot more reactive than cold and pulls all sorts of crap from the metal pipes with it. For example lead piping was still used in some parts of Russia in the 90s. You would definitely not want to drink hot water that ran through that. 

If you have a fairly modern local water heater and plastic piping between the heater and the tap, it makes no difference.