This is a completely free and open-source Water Tracker and Reminder application. No subscription; no in-app purchase; no user data collection, no ads, no gotchas of any kind!

+ Super simple & quick drink logging.
+ Smart Water Reminder after 2 hours of each drink logging. NO REPEATED & ANNOYING reminders again and again.
+ Water Summary with 24-hour view or weekly view.
+ Data synced with, and only with CloudKit and HealthKit. No user data collected to me in any form.
+ Flexible daily goal setup.
+ Support both Milliliter and Ounce.
+ Widgets for Home Screen.
+ Deep integration with Apple Watch.

This application is open source in: https://github.com/SteveLeungYL/WaterTracker. 
If you link this app, please consider giving me a star!