Little bit of water under plastic cover on my shimano shifters
You don't need to worry about that.

There are nearly no components on your bike -- except for the hub and bottom bracket bearings -- that are sealed to be more or less waterproof. Most of the components are totally fine with water on or in them.

Especially for your shifters: their internals are mostly made out of plastic so no need to worry. As they are built in some half-closed way, there may be some water condensation in some corners, which is no real problem. The water may disappear as soon as the weather is warm enough and the bike stands in the sun for some time. It also may reappear, but as said, it's not a real problem, just some matter of optics.