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Thread: Is it normal to use this much water all at once?

  1. #1

    Default Is it normal to use this much water all at once?

    Hi,
    This is a very broad ballpark question. We have about 18 rotary Hunter sprinkler heads for larger areas of our lawn and about 12 Rainbird static heads for smaller areas. Here's what the watering session looks like:
    6 rotary heads run for 35 min
    6 rotary heads run for 35 min
    6 rotary heads run for 20 min
    6 static heads run for 10 min
    6 static heads run for 10 min
    After the system is done running it uses over 3000 gallons of water in a single session. Does this sound right? This is about what we use during the entire month in winter!

    A gentleman who owns an irrigation company told us the system with these heads should use from 1800 to 2200 gallons per session. He didn't see the actual system, we just exchanged emails through a mutual acquaintance. He recommended inspecting our system for leaks or checking the seals on the heads.

    We checked for leaks, and didn't find any. The water meter stays still if the system isn't operating. If we leave the house and spend a few days elsewhere and no water is used at all, then our meter would stay on the exact same mark as we left it. There are no soggy spots anywhere in our lawn after watering it. So unless the leak occurs deep under ground during the 110 minutes when the system is actually running, and the 5-gallon-per-head average rule is correct, then 3000 gallons should be correct. Or is the gentleman right about 1800 to 2200 gallons?

    We can reduce the flow on all those heads to get it down to 1800 gallons, but then the lawn would receive very little water. Far less than recommended 1 inch. Actually it already gets a little less than that. What are we doing wrong?

    Thanks for your help!
    Last edited by Amy_2009; 08-04-2009 at 10:39 AM.

  2. #2
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by Amy_2009 View Post
    Here's what the watering session looks like:
    6 rotary heads run for 35 min
    6 rotary heads run for 35 min
    6 rotary heads run for 20 min
    6 static heads run for 10 min
    6 static heads run for 10 min
    After the system is done running it uses over 3000 gallons of water in a single session. Does this sound right?
    Let G = gpm for each head, assuming static and rotary heads deliver the same GPM.
    6Gx35 min +
    6Gx35 min +
    6Gx20 min +
    6Gx10 min +
    6Gx10 min = 3000Gals

    Simplifying,
    6G(35+35+20+10+10) = 3000Gals
    G = 500 gals/(110 min) = 4.5 gpm.
    Each head should fill a 5 gal. bucket in 1.1 minute.

    Normal rainfall for me is 3"/month, ~0.1"/day. What area are you covering?
    3000 gals = 400 cu. ft. = ~1 acre to a depth of 0.1".

    Normal water usage per person per day is 100 gals.

    Hi, Amy. . .
    Last edited by Thatguy; 08-04-2009 at 12:59 PM.

  3. #3

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    Ok, thanks!

    Quote Originally Posted by Thatguy View Post
    What area are you covering?
    About 13,000 square feet.

  4. #4
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by Amy_2009 View Post
    Ok, thanks!
    About 13,000 square feet.
    12(400)/13,000 = 0.4" depth of water over this area, so in my neck of the woods you'd do this 3000 gal watering every 3 or 4 days.

  5. #5

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    Right, but does it sound likely that all these sprinklers CAN use 3000 gallons over 110 minutes? Or should it actually be using around 1800~2200 as the guy said?

    Sorry if I wasn't clear: the question wasn't how frequently should we water using the existing settings (although your info is useful, thanks!!), but rather "is the system really losing water because 3000 gallons is too high for that many heads over 110 minutes?"

    I'm trying to figure out if there's really a leak somewhere, or maybe he just quoted a lower number in hopes that we'll hire them to do the inspection, etc.

  6. #6
    Homeowner Thatguy's Avatar
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    Quote Originally Posted by Amy_2009 View Post
    Right, but does it sound likely that all these sprinklers CAN use 3000 gallons over 110 minutes? Or should it actually be using around 1800~2200 as the guy said?

    Sorry if I wasn't clear: the question wasn't how frequently should we water using the existing settings (although your info is useful, thanks!!), but rather "is the system really losing water because 3000 gallons is too high for that many heads over 110 minutes?"

    I'm trying to figure out if there's really a leak somewhere, or maybe he just quoted a lower number in hopes that we'll hire them to do the inspection, etc.
    Your meter says there is no leak, at least when the system is off.
    Measure the outputs of the static and the rotary heads by filling a bucket. The math should work. If it doesn't, there is a leak when the system is on.
    With this many outlets, pick two or three at random for testing from the static group and the rotary group.
    Last edited by Thatguy; 08-04-2009 at 04:17 PM.

  7. #7
    Moderator valveman's Avatar
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    Bottom line, either way you need a lot of water. If you have the option to drill your own well, you could pump water for a fraction of the price you are paying for city water.

  8. #8

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    Quote Originally Posted by Thatguy View Post
    Measure the outputs of the static and the rotary heads by filling a bucket, pick two or three at random for testing
    Excellent idea, we'll do that. Thank you!

  9. #9

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    Quote Originally Posted by valveman View Post
    If you have the option to drill your own well, you could pump water for a fraction of the price you are paying for city water.
    Yes, I know No such option for us unfortunately. Our friends out in the country have their own well and they water all day long.

  10. #10
    Plumber jimbo's Avatar
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    Seems like the 3000 gallons pecils out as just about exactly the right number. That is right at 4 HCF, and here in San Diego, that woudl cost you about $30 every time you watered that golf course! Of course , the mayor would also publish your name on the website as a water guzzler!

  11. #11

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    Quote Originally Posted by jimbo View Post
    in San Diego, that woudl cost you about $30 every time you watered that golf course!
    Wow, that is high. Our rates are much lower here in Oklahoma. But (unlike San Diego?) once it gets hot here it stays hot for a while. So you either keep on watering and watering, or your grass starts to make crunching sound when you walk across your lawn.

  12. #12
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    Amy,
    It could very well be correct. You should first check and see what size nozzle is in each head. Hunter nozzles have a number stamped in them. That number will correspond with a flow in gallons per minute at a specified pressure. If you have a idea of what the pressure may be at the base of the head you then would cross reference it on a Hunter sprinkler head chart and that would give you the approx. flow from the head. Then you need to do the math.
    Example:
    Lets just say each head , both spray and rotary has a nozzle that puts out 4 gpm at 45psi.

    zone #1 6 rotary heads @4gpm each x 35minutes = 840 gallons
    zone #2 " " " " " " " " = 840 gallons
    zone#3 6 rotary heads @ 4 gpm each x 20 minutes = 480 gallons
    zone #4 6 fixed spray heads @ 4 gpm each x 10 minutes = 240 gallons
    zone #5 6 fixed spray heads @ 4gpm each x 10 minutes = 240 gallons

    Add the total gallons up ( 2640 gallons ) and you can see that it is very possible to use that much water in one irrigation cycle. Now, this is just an example and your nozzle sizes may be very different from my example. If they are smaller and putting out less water then maybe you do have other problems in the system as far as leaks. A full circle spray head with a 15 foot radius puts out approx. 4gpm at 30 psi, so if they are half circle heads then the output would be approx. 2 gpm. You could have a mix of nozzle sizes based on their arc, weather it is a quarter circle, half or full cirle head. If you like, provide the brand and model of the rotary and spray heads and if possible the nozzle sizes and I can check the charts.

  13. #13

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    Wow, thanks! Lots of interesting info. I'll get those numbers today. Thank you!!

  14. #14

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    You need an Irrigation Audit. Where do you live? Send me a plane ticket and buy me a couple rounds of golf and I'll have your answer!

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