There are a few people I work with who are very passionate about coffee, which is something I enjoy very much as well, and have been known to geek out on.
Recently, I passed around this video from Sweet Maria's, which is one of the bean providers the most enthusiastic of said co-workers shops with.
The Sweet Maria's gent claimed as an aside in that video (which really raises the bar on coffee geekery, truly impressive) that one should always weigh one's water, as the volume changes when it is heated.
I get that the volume changes, but it seemed to me that it can't change that much. I realized this weekend that I had a way to find out exactly how: WolframAlpha. I just had to ask it Volume of 1kg of water at 90 degrees Celsius and, lo and behold, it knows!
Curious, I punched in a few more numbers, and made the following chart:
So the water expands a pretty impressive 3.5% on it's way from "very cold" to "coffee temp". Assuming you start with water which is not totally chilled, however, the expansion starts to become less of an issue.
So, does it matter to most of us -- no. We probably don't measure our water within 3.5% accuracy on the best of days, anyway. (And if you have a hot water machine, like we do, which happens to dispense perfect temp water anyway, you're measuring pre-expanded.)
But if you're making any kind of serious volume, 3.5% might actually start to have an impact. It's at least a sip out of a cup.
I'd say we have to call this geek "Plausible." But I'm still not weighing my water.
Aside: if anyone knows how to use WolframAlpha to actually make a chart like this, let me know. It seems like it should be doable, I just couldn't finesse my query in such a way to make it happen. OmniGraphSketcher to the rescue.