The FA forgot to load the water.
There may have been no water on board - BUT it had nothing to do with the FA.
What happens is the FA board the aircraft, at about the same time - the catering truck arrives and and carts are loaded, the FA then place the carts in their places and do whatever they need to do pre departure before boarding the pax and doing the safety briefings etc.
So if there is no water or no ice cream or no napkins - etc - its the fault of the caterering trucks not the FA.