Sediments, schmediments

I started work here on March 14. That's exactly 5 months, 1 day ago.

Since then, I've drunk about 1 liter of water per work day, straight from the filter.

And now, I'm wondering how many grammes of strange black substance I've inadvertently drunk because of my gulping habit and use of a dark-coloured container before this.

I started drinking from my white mug instead of red bottle last week. Usually, my habit is pour and gulp, pour and gulp.

Today, I poured and walked off to do something away from my desk. Came back and was about to gulp when I noticed black sediments at the bottom of the cup.

Blasted air-conditioner must be spewing dirt, I thought, and went to give white mug a lather and rinse. Poured again. Water was crystal clear.

Decided to experiment by leaving mug on other side of desk, far from aircond, for another half hour.

And behold, look thou at the bottom of thy cup! Sediments! Icky black sediments that make thy mouth feel gritty even though thou hath not even taken a sip!

Ish. I'll just bring a huge kong of water from home every day from now on.

By the way, has anyone ever questioned why those things are called filters? What is this action called "filting" that they do? What do they filt? Is it water (in the case of water filters) or impure particles in the water? If it's the latter, shouldn't they be called "Icky Particle Filters" rather than "Water Filters"?