20kgs of water sounds right to me, some years ago cycling from Egypt to Uganda, I had to ride across the Nuba Desert from Wadi Haifa to Khartoum, I loaded up with 5 gallons of water and used that up easily and had to top up in a couple of villages when I I found them. unless you have ridden in desert conditions peeps don't understand just how much water a body uses up when you are working hard and any wind just make it worse.