Mineral water contains carbonic acid which is what dominates the taste of mineral water so that's why it can taste sour or bitter to some people.
Also each mineral in the mineral water has different characteristic tastes of it's own which can lead to the bitter tasting of the mineral water.
And when the mineral water has sodium combined with chloride then the mineral water can get a more salty taste to it.
It's normal though for mineral water to be bitter tasting or salty tasting and it's usually a taste that people have to get used too if the person hasn't drank any mineral water before.
I hate mineral water myself but some people enjoy it.