Hello @Jogger1941 and welcome to the Community. There is a bug in the Fitbit app that doesn't let us log water using the green "+" button. Please tap on your Water tile, then the "+" option in the upper right. Now you will see the log page with the Save/Cancel options.
Fitbit is aware.
Laurie | Maryland
Sense 2, Luxe, Aria 2 | iOS | Mac OS
Take a look at the Fitbit help site for further assistance and information.