Introduction

Global urban water utilization by people increased over 20 times in 100 years. In 1900, it was 200×108 m3; in 1950, it was 600×108 m3; in 1975, it was 1,500×108 m3; and in 2000, it was 4,400×108 m3 (Bao and Fang 2007). It is predicted that urban water utilization by people in the year of 2050 will equal total global water utilization in 2004 (Song et al. 2004).