Coffee made in Bodum vacuum pot tastes bad.

My son has a Bodum vacuum pot that he's used for about a year. At
first the coffee tasted good. He said the coffee lately has either
been tasting bitter or has no taste at all. He uses bottled water and
the same coffee he's always used. He changed the filter and that
didn't improve the flavor. He did mention the coffee was taking longer
to brew than normal. He grinds the beans the same amount of time as
before. Any suggestions on what he can do?