@mingocr83
A lightning system will indicate the stage of water usage
Yes, lightning would certainly make you want to get the soap off fast!
I believe they opted for lighting instead.
I heard the same 500kg figure for the water carried. That's only enough for the 14 1st class pax to shower once. They initially looked into shower availability for all 90 upper deck pax, but realised that they would need to filter and recycle the effluent to achieve that and decided against it!