One of my brother-in-law's coworkers claims that drinking hot water (straight from the tap) aids in digestion. I've been able to find a debunking of cold water causing cancer, but can't find anything related to drinking hot water (at least nothing backed by scientific evidence, or even the appearance of scientific evidence). So, is there any truth to this claim?
There is some scientific evidence that the temperature of meal/drink has an effect on digestive system activity. See Effect of meal temperature on gastric emptying of liquids in man:
Anecdotally, in my experience, drinking half a liter of hot water (boiled cold tap water) feels like it has an effect on digestion, but I wouldn't claim that it aids digestion. This is so easy to try out for yourself that I'd suggest doing so.
Drinking hot tap water is not recommended. I guess it might have an effect on digestion too, depending on the plumbing and water quality. I hope this isn't the effect the claimant feels is aiding digestion.
Here's Dr. Steven Novella's take on this issue at the Neurologica blog: