Suppose you had 32 sq. ft. of raised bed growing space. Here's how to calculate how much water each 32 sq. ft. bed would use per day. Multiply the number of emitters times the rated gallon per hour (GPH) for the drip line. In a four four by eight foot raised, one 32 sq. ft. bed would have five lines with 11 emitters each. That's 55 emitters total. Each emitter drips .57 gallons of water per hour. Here's the math:
- 55 emitters x .57 GPH = 31.35 gallons of water per hour
- 31.35 gallons / 6 = 5.23 gallons of water for 10 minutes
- 31.35 gallons / 60 = .523 gallons of water per minute
Remember that an hour has six 10 minute intervals and 60 one minute intervals. Therefore, you can figure exactly how many minutes you need to water and note how much water you're using. Keep in mind that none of the water is being wasted! Every drop goes to the roots of your veggie garden.
It's also worth noting that drip lines are metered. Drip tape isn't. Drip lines are the solid lines with the built-in emitters. At any rate drip line operate under low pressure, usually between 15 and 25 psi. This means the emitter at the top of a hill will get the same amount of water as the emitter at the bottom, even distribution. This important because you don't want water flooding one end of the garden while the other end is bone dry.