“a bit of" is used for uncountable nouns. For example "a bit of water". In Chinese, this would be "一点水”. Saying "a few water" would be like saying "一些水". Water can't be broken down into specific quantities so you used "a bit". However, you could say "a few cups" because cups are a countable item. This would be like saying "一些杯子“. On the other hand, in some cases, Chinese is more complicated. To make the contents of the cup specific to water, you need to say "几杯水“, however, in English you can simply say " a few cups of water". Hope this helps!