Water Flow – Penstock

Water Flow

Water flow is a measurement of the quantity of water flowing past a given point in a period of time and is measured in volume.

The volume of flow is typically expressed in gallons per minute or liters per minute.

The easiest way to measure water flow is to channel the flow of water at the natural speed of the flow into a container with a known volume.

Then, you measure the time it takes for the container to be filled with water to calculate the flow rate.  Be sure to make several measurements at different times of the year to calculate the average water flow rate, as the flow rate may change with the season.

If you are in a zero head height location, one technique to measure water flow is to throw a ping-pong ball in the flowing stream, if you can keep up with the ball while briskly walking, the flow is too slow.  If you need to quickly jog or run to keep up with the ball, then the flow rate will probably be high enough to use a zero head water turbine.


A penstock is what controls the rate and volume of water flow from a water source towards a hydro turbine generator.  It is usually designed as a closed pipe with opening and closing gates to allow only the desired amount of water into the system.

When a hydropower system is not being used, water can be stored in the penstock for later use.