The numbers of those living on less than $1 a day (1.2 billion worldwide)
coincide approximately with the numbers of those without
access to a safe drinking water supply (1.1 billion). The numbers of
those living on less than $2 a day (2.8 billion) coincide approximately
with the numbers of those without access to safe sanitation (2.4 billion).
At present, there is no way of knowing whether this symmetry is
causal or coincidental.