Is there a way to initiate a programmamble action without opening an app?

I'm trying to find out if there is any way I can keep track of glasses of water I drink with the absolute minimal interaction with the watch.

My ideal scenario would look like this:

1) I drink a glass of water, I long-press the START hot-key

2) A number on a watch face under the time increases by one

Is anything like that possible? I've only seen widgets or apps that need to be opened, I would much prefer a single-key solution.

This should work with or without any activity running, if possible

Thank you!