h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Here's the situation: my office is not close to a source of hot water, so I've purchased a small (1 qt) electric pot to heat water in for tea. Every morning when I get to my office, I take my pot to the restroom and fill it with city tap water, return to my desk, plug it in and, in about 3-5 minutes have boiling water for tea.

Yesterday afternoon I decided I wanted a second cup, but was too lazy to walk all the way to the restroom for the water, so I filled the pot with bottled water that I keep in my cabinet just for that purpose. As I was drinking my tea I noticed a lot of film on top that was sticking to the sides of my cup as I drank.

I've noticed this before when I use different tea bags, but not so much with my regular brand. I thought it was the tea causing it. But it might be the water?

I suspect it is the water, I get it at home when using tap water and we live in a hard water area.

Agreed. Mr D has already said what I would have but to expand a bit.

From what you report the water in your office is probably soft (no mineral content). The bottled water will be mineral water and these have a high mineral content that will precipitate out causing a scum film on your tea.

I grew up in a hard water area where the hardness was chalk and the film was present on everything. Chalk is murder on all heating elements as it leaves a heavy, furry deposit. I spent a few years in an area with limestone hard water which leaves a thin, stony deposit but still causes a film on tea.

Where I am now the water is very soft, so soft in fact that the dishwasher does not need any salt or softeners and kettles last for years.

t.

Ok.

For a bit of variety this morning I got cold water from the water cooler instead of the restroom. The water cooler is supplied by the same company that supplies the individual water bottles. No film today. Is it because there's a filter on the cooler?

Hard to say but it might be that the water cooler bottles are filled from the local water supply and filtered and the bottled water is a mineral water from a different source.

t.