In his 2011 book Brahma Chellany reports:
…Singapore has pursued demand management through greater water productivity and efficiency. By plugging system leaks and inefficiencies and raising the price of domestic water, with the tariff and tax rising steeply after the first 40 m3 a month, it managed to reduce household water use by about 10 percent since the mid-1990s to about 155 liters per person per day in 2011. That consumption level is nearly four times lower than that of an average American.
That is from Water: Asia’s New Battleground, which is actually one of the most interesting political economy books published in the last few years.