Much and many can be confusing – it’s all about countable and uncountable (or measurable) nouns. You can count raindrops (if you’re fast!), so you use “many” when referring to them. But you can’t count water. You can measure it, by the cup, or the litre, so in this case you use “much”.
Confused about when to use less or fewer? There’s a rule in English that we treat countable nouns and uncountable nouns differently. This comes into play for fewer and less. If we’re talking about countable nouns – things you can count – we use fewer. Ten items or fewer (we can count the items); fewer … More Less and fewer