Allison Arieff writes in a New York Times blog that,
"… a recent short hop I took on Horizon Air set a new dismal standard for cost efficiency.
The lavatory had no sink.
Ick.
It did have a lone plastic bottle of hand sanitizer glued to the counter" (right, photo by Bryan Burkhart).
While the water in sinks is not for drinking, I can think of lots of scenarios — and have even experienced a few — where water and paper towel is essential for cleanup on an airplane.