Millimeters over what area, though? [Edited] It could be any, if the device depends on area. The more area you use, the more water you get. Weather report oft

Millimeters over what area, though? [Edited] It could be any, if the device depends on area. The more area you use, the more water you get. Weather report often uses litres per square metres. One meter high per square metre is a thousand litres, so one mm would be a litre. Edit: in the article I read: These small, initial test systems were only designed to produce a few milliliter. So it's much less :-)