How much water does a 3000ml hydrogen-oxygen machine need to add each time?

The machine will prompt that there is a lack of water when it is turned on for the first time. Press the water filling button and add about 3.5-4L.
The machine will prompt that there is a lack of water on the screen when there is a lack of water in the future.
Press the water filling button to add water automatically. Add 1.5L of water each time, and the machine will retain 2.5L to protect the machine.