An average family of four uses roughly 1200 liters (about 300 gallons) of water per day. (one liter = 1000 cm3.) How much depth would a lake lose per year if it uniformly covered an area of 43 square kilometers and supplied a local town with a population of 43000 people? Consider only population uses, and neglect evaporation, etc. Where do I even start?

well... 1200 liters/four people = 300 liters/person times 43000 would be 12900000 liters/day 1000 liters = 1 cubic meter : 12900000 liters/day = 12900 m^3/day 1000^3 m^3 = 1 km^3 : .0000129 km^3 1.29 *10^-5 / 49 km = 2.63 * 10^-7 = .263 m (meh, got kinda lost in the algebra) but as a check... .263 m times 49000000 m^3 = 12887000 it checks

slayerdeus, 1 liter is 1,000 cm^2 x 1 cm deep 1,200 liters is 1.2E6 cm^2 x 1 cm deep 43,000 families is 5.16E10 cm^2 x 1 cm deep per day Error. Population is persons not families 1 Km = 1,000 m x 100 cm = 100,000 cm 1Km^2 = 1E10 cm^2 43 Km^2 = 4.3E11 cm^2 Use Rate/Supply = (5.16E10/4)/4.3E11 = 0.03 cm/day or 0.0118 inches/day or 84 days per inch or 4.3 inches/year.

300 l per person/day * 43000 = 12900000 l / 1000 = 12900 m^3/day 43000000m^2 to a depth of 1m = 43000000 m^3 43000000m^3 / 12900 m^3/day = 0.0003m/day 0.0003m/day * 365 = 0.1095m/year = 4.3 inches/year OK, so I get the same correct answer as MacM, but it's so fun!