What is the density of water?

The density of water is dependent on its temperature, but the relation is not linear and is not even monotonic.

Temp (°C) / Density (kg/m3)
+100 / 958.4
+80 / 971.8
+60 / 983.2
+40 / 992.2
+30 / 995.6502
+25 / 997.0479
+22 / 997.7735
+20 / 998.2071
+15 / 999.1026
+10 / 999.7026
+4 / 999.9720
0 / 999.8395
−10 / 998.117
−20 / 993.547
−30 / 983.854

Please refer to this article on Wikipedia:
http://en.wikipedia.org/wiki/Water_%28molecule%29#Density_of_water_and_ice

density of water is nearly 1g/cm^3 for simple calculations. It is maximum at 4 degree centigrade.