Q. My pump produces 10 GPM at 45 PSI or 7 GPM at 65 PSI. Do you think the flow is decent for my yard? When I had pro’s quote my job (which is why I’m doing it my self as the numbers were huge) they all said I’d need about 40 sprinkler heads.
A. My gut feeling is that you don’t have enough water capacity from your pump and/or well to irrigate the size of area you have planted in lawn. (Don’t panic yet, keep reading for some suggestions.) 40 sprinklers would be a lot to try to run off of 7-10 GPM of flow. But it depends greatly on your climatic location and water needs. If you only need irrigation for periodic supplemental watering you may be OK. The rule of thumb is that 10 GPM will water about 1/2 an acre of lawn, assuming you need to water about 3 times a week to keep the grass lush. So if you need to water only twice a week, then you could water more area with 10 GPM of water flow. Also, the rule of thumb assumes you only wish to water during the night hours. You could water more area if you are willing to water 24/7 during the peak hot season. Keep in mind that if you share the water use with your house that 24/7 watering might not be a good idea as you won’t have any water left over for use in the house. When your spouse gets in the shower and no water comes out because the sprinklers are using all of it, things are not going to be pretty!
The rule of thumb is that it takes 20 GPM to water an acre of lawn in a hot climate area. So if you have a larger lawn you may need to think about adding a new pump and/or well. I really don’t have enough info to say for sure since I don’t know the size of your yard or your climate location. Take a look at this article which will show you how to calculate how much water you will need for your exact situation:
Options to consider if you don’t have enough water:
An option a lot of people in rural areas use is to create watering zones around the property. They heavily water the area right around the house, possibly 25′ or so out from the foundation, sufficient to create a really lush green lawn. Then for the next 25-50′ out they apply just supplemental water, watering maybe once (or twice) a week in hot weather. This supplemental water area would tend to yellow a bit and show stress during the hottest part of the year. Then they have a “no irrigation” area at the far reaches of the property that gets no irrigation water at all.
Tips on designing supplemental water areas: The sprinkler system design for a supplemental water area should be the same as for the lush area. In particular, the distance between the sprinkler heads should be the same for both the lush and supplemental areas. The only difference is that the supplemental area doesn’t get watered as often. Don’t try to stretch out the sprinkler spacings to use less heads in the supplemental area, that will result in problematic dry spots that create a splotchy look to the grass. A splotchy lawn really looks bad. If you space the heads correctly then you will get a uniform looking lawn in the supplemental area, it will just have a yellower tint to it, and it will not be nearly as noticeably “ugly” as a splotchy lawn. Also by designing the supplemental area for “full water coverage” you have the future option of turning that area lush by simply adding a new well or bigger pump. If you skimp on the sprinkler spacing it is really difficult to correct the spacing problem if you ever wanted to make it lush. You can add more heads, but I can tell you that over my 35 years in the business I have never had a customer who was happy with the results of adding more heads. Your only real option to fix a system with heads installed too far apart is to rip it all out and start over. Expensive!!!
Another option: If you don’t have the water supply or money to do all of it right, then install it in phases. Start with the area around the house. Then add more sprinkler zones to water the areas farther out from the house each year as you have funds and time. Add another pump and/or well later when you need the water. The critical thing is to “do it right” in regards to the sprinkler spacing and resist the temptation to stretch spacings between the heads to stretch the water supply or save money. The results are always disappointing if you do that.