1 Sources and Quantity of Water

The sources of a water supply may include rainwater, surface waters, and groundwater. During the water cycle, rainwater recharges the surface waters and groundwater. River, stream, reservoir, and lake waters are major surface water sources. Some communities use groundwater, such as wells, aquifers, and springs as their water supply sources.

Runoff refers to the precipitation that reaches a stream or river. Theoretically, every unit volume of water passing the observation station should be measured and the sum of all these units passing in a certain period of time would be the total runoff. However, it is not available due to cost. Observations should be carried out at reasonably close intervals so that the observed flow over a long period of time is the sum of flows for the individual shorter periods of observation and not the sum of the observed rates of flow multiplied by the total period.

Example 1

Records of observations during a month (30 d) period show that a flow rate 2.3 cfs (0.065 m ³/s) for 8 d, 3.0 cfs (0.085 m ³/s) for 10 d, 56.5 cfs (16.0 m ³/s) for 1 d, 12.5 cfs (0.354 m ³/s) for 3 d, 5.3 cfs (0.150 m ³/s) for 6 d, and 2.65 cfs (0.075 m ³/s) for 2 d. What is the mean flow rate?

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