How to Measure Flow in a Drain

The stream of water coming out of your kitchen sink is clearly different when you open the tap halfway than when you turn it on full blast. You express how much water moves through the tap as "flow," the volume of water that passes through an opening in a given time. Measurements of flow are commonly recorded for tubes or rivers, over a distance, by comparing the relative pressures. However, in the case of a drain, you can measure flow by controlling either the volume of the water or the time that it flows, and measuring the other factor.

1-gallon container or 2-liter bottle
Bucket or other wide-mouth container
Stopwatch
Water
Partner

Instructions

- 1
  Fill either a 1-gallon container or a 2-liter bottle to the brim with water: Select whichever container offers the more practical unit of measurement for your purposes. Transfer the water, without dripping, to a large bucket or other wide-mouth container.
- 2
  Clear the sink, shower or other area surrounding the drain. Have a partner hold the bucket of water over the drain. Have the partner dump the gallon of water into the drain. Start the stopwatch at the same moment. Stop the timer immediately when all of the water has passed through the drain.
- 3
  Repeat the same procedure at least two more times. Repeat another three times, switching roles with your partner, if your times vary widely. Divide the volume of water you used by the time that's passed. Adjust the measurements as necessary; for example, if you use a 2-liter bottle, you'll have to divide your time reading by two to arrive at the volume in liters per second. Find the average time from all your trials and use that as your flow measurement.

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