Ezekiel 4:11

“And you will drink water by measure, the sixth part of a hin. Each day at the same time you will drink it.”

As for food, so for water. He was allowed a little over 0.6 litres (a pint). This was hardly survival rations, but would often be necessary when under siege with water difficult to obtain. It may be that he was allowed to supplement it out of hours when not under observation, but that this was his general practise seems to be of some doubt. The purpose of the rations was to simulate siege conditions in the eyes of the people.