Can I log water straight from the reminder?

Yes. Water reminders have buttons for the cups you use most and Remind me in 30 min, which never rings in your quiet hours. A tap logs the cup on your phone at once (it syncs when you are online) and the reminder shows your progress, like +250 ml · 1.5 of 2.5 L; once you reach your goal the reminders stop for the day. For any other amount, tap the reminder on Android to open a small Log water window over the screen you are on, or press and hold it on iPhone for a slider with your progress ring.