Two billion litres a year. Impressive number at first glance. But let's say my own household of 4 was able to keep water consumption down to 500L/day (I wish)

Two billion litres a year. Impressive number at first glance. But let's say my own household of 4 was able to keep water consumption down to 500L/day (I wish), that's already around 180K litres/year just for my house. So divided into 2B, that's about 11K houses' worth of wastewater. A modest size town's worth, for all the air travel worldwide.