An umbrella is to protect you from the rain. It’s not a weapon to harass fellow citizens.
When entering buildings or any indoor place, always close your umbrella before you go in the entrance.
It’s said that walking into an indoor place with an open umbrella is bad luck. It is also bad manners. There’s no need to block the entrances with your umbrella. Half close your brolly, give it a swift shake, then close up completely. Now you can go inside.
The same rule applies when heading outdoors. Open your umbrella when you get outside of the entrance.
A little water is not going to hurt you.