Three years and still no Gallons per Hour?


OK, so here’s the rub: I have seen that as far back as April of 2013 people have been asking for a selection of Gallons per Hour. How hard can that be? It is completely obvious that Rachio designed there system to water lawns with sprinklers and not to water a drip irrigation system. Their answer to the problem of inputting Gallons per hour is to convert it to Inches per Hour with the following formula:

PR = (96.25(A*B))/©
96.25 = constant that converts gallons per minute (GPM) to inches per hour. It is derived from 60 minutes per hour divided by 7.48 gallons per cubic foot. times 12 inches per foot.
A = #heads -or- #emitters
B = flow rate (GPM) per head -or- emitter
C = zone square footage

Now, I actually am an engineer and I can kind of understand this stuff. BUT what is this “C = zone square footage” stuff all about? In an drip emitter landscape, what doe is mater what the zone square footage is? I may have a 1000 square foot yard but only have one plant in the center of it being watered. Or more realistically, I may have a 1000 square foot yard with 20 plants but they certainly do not cover the whole yard. So why is the C term even there? And why should I have to convert in the first place. I thought that was what computers are really good at and that simple arithmetics should be something that could be implemented in, say, a minute or two?

Without being able to enter the number of emitters and the gallons per minute the rest of your software is completely useless. Even if I bother to run your calculations (which I have) you system spits out completely inadequate and inaccurate watering schedules because it still thinks it is watering a lawn.

So, come on Rachio, your customers have been asking you for three years now for Gallons per Hour and so far you have been ignoring them. When will you actually listen to them and give them what they have been asking for? You tell them that you care about what they think, but for the past three years, at least, you haven’t.


Well first off, you need c to define uniformity to you velocity. Throwin 5 gallons an hour on 2 square is vastly different than on 10 square feet. So I hope you can take it from there, if rachio knows you need .75 inches of water, they need to know the rate per foot so they can compute how long to run.

As far as drip goes, I don’t know. I have lots of drip and still can’t mathematically prove the square footage portion of a model. So I’ll assume that is why we don’t have a gallon per hour, not sure.


Thanks for your comment. I am not sure you understood mine. My point was that if I am using a single point emitter with a constant flow rate, then the area does not matter. One single emitter is not going to water 10 square feet. It’s going to be hard put to water one square foot. But it will water the single plant that it is placed at rather well. I need the water to go down to the roots, not out where it will evaporate into the air. That is the whole reason for using emitters and not drip lines or sprinklers. That is why the calculation based on square feet is completely useless. I have checked with several horticulturalist and they all agree.

My other point is that since the very inception, people have been asking Rachio for a way to enter number of emitters and emitter flow rates in gallons per hour. I am certainly not the first. A quick search of this forum will show many requests. It seems rather disingenuous for Rachio to say “We will consider your request in our next update.” because obviously they haven’t.


@Boris I’m with you regarding how it would be much simpler for those of us with single point emitters to have them defined by GPH, then being allowed to input how many of them are in a zone. For that matter I wouldn’t mind if I even had to put in a GPH number for the whole zone.

My guess is that since the algorithms for watering are based on inches of water applied, the algorithm would need GPH translated to in/hr anyway for the algorithm to work. As you mentioned, the tool could do it for us, but without an algorithm change the area would need to be defined properly or our watering time would get screwed up. On a single point emitter that area calculation isn’t so obvious. A 1ft x 1ft area is often recommended by Rachio for the estimate, but I disagree with that recommendation. Online calculators that I’ve found assume equally spaced grids of emitters, which isn’t valid for single point emitters, or even if you have a few on a tree or shrub.

As it stands now, the only impact the area calculation has is to the water used. With a definition in in nozzles of GPH it would also affect watering duration. Of the two choices I would rather only have it the way it is now since it doesn’t affect the watering time.

It seems to be a more complex problem than meets the eye, and perhaps that’s why it hasn’t been implemented? I do think it’s a more significant point of confusion than Rachio might realize, as they may not be aware that many markets are dominated by our type of irrigation style. Three of my four zones are single point emitter setups. I also know they have a lot of development on their plate, so some things keep getting pushed off, without a deliberate attempt to ignore or deceive.

Having said all of this, the link below shows how I back calculated the area calculation in a single point emitter setup to get reasonable water estimates. I took the resulting area then plugged it back into the water usage equation and got the GPH/emitter * num_emitters value that I expected, so I think it works. You have to know how many gallons you want to put down, then set the PR accordingly. After that, do the back calculation.

Sqft for whole yard drip zone?

I hope this helps, and thanks for bringing it up. It helps raise awareness to the issue.


Another problem that I have is that I have many different emitters in the same zone. 1/2, 1, and 2 GPH. Have no idea of the best way to calculate that out. And with roughly a 100 emitters per zone, at this point I haven’t been game to go through and take each one out to see what it is and document them all. So even GPH wouldn’t help me.

I’m thinking that what I really should do is get a moisture sensor, check levels before watering, water for a set amount of time, check moisture levels again and see how far the water goes down? Think that would work? But I have to admit that all I know about moisture sensors right now is what I’ve read on the forums here. (I’ve learned so much, and I realize that I still don’t know anything!!! But it is so much fun!)


Here’s another post that may be useful.

We have a great “Water it Wisely” website in Phoenix that guides us to how long to run a zone, and how often, given a GPH flow rate. It’s what I used to determine my run time.

After that I set a PR in in/hr to get the run time that I wanted, then back calculated the area based on my previous post description in this thread. My thought was if this manual approach I used could be automated it might solve the problem that you’ve noted. Something like the “Water it Wisely” algorithm of determining run time based on GPH instead could be used instead of the existing in/hr metric would eliminate the need to enter area for single point drip zones. The Rachio guys would need to determine applicability to other climates, then find a way to apply the ET changed throughout a season. It’s not a slam dunk and would require some work but the concept is there.


I just did this for one of my tree zones and I’m pretty happy with the schedule it popped out. Thanks for the suggestion


I have a zone with a bunch of emitters like this as well although not nearly as many. Maybe around 50. I have to replace each emitter though because they installed the flag emitters that don’t compensate for pressure so they could be outputting any amount depending on what the pressure is at the emitter. I plan on calculating how long to water my least drought tolerant plants then use that time to calculate the appropriate emitter for my drought tolerant ones. From there I’ll just use @azdavidr 's method to determine the PR to put in the zone settings.


@JPedrego. Which part did you use, setting the PR to get the duration recommended by “Water it Wisely”? Glad to hear it worked for you. Sometimes I wonder if it just happened to work out in my case, so it’s good to hear that it worked for someone else.


@JPedrego. I didn’t realize that some flash emitters compensated for pressure. Do you have a link that describes them or has a picture?


@Linn. That’s a tough one. With that many emitters it would take a while to optimize. I don’t have that many and still haven’t found the time to check them all, although I’ve been wanting to. I feel like I should just commit to checking one shrub or two per weekend.


@JPedrego and @azdavidr, I didn’t even realize until these forums that I needed pressure compensating emitters. Turns out that the ones that I’ve bought myself are, and I’m guessing that the ones the first irrigation guy put in are not. So later this fall, I think I’m going to buy enough to replace everything, and then commit to doing 10-20 a day, and actually keep careful track of what I replace. So maybe next year I’ll be in a better position to get everything dialed in better.

My biggest fear right now is that I’m traveling a lot the next couple of months and can’t see what’s wilting. Just hoping I have it tuned well enough that the majority will survive. It’s tough with this Dante weather and the 10-20% chance of rain predicted every afternoon that actually only happens 10% of the time. :confused:


Yeah I used the watering time from the brochure to fine tune the PR.

These emitters from home depot are pressure compensating

If you installed the emitters yourself you are probably using pressure compensating ones. The ones originally installed on my system are like these


@Linn. I could understand the nervousness of not monitoring your vegetation while traveling. You could always bump up you crop coefficient a tad while your gone. It won’t be optimal, but might be a bit safer to be watering a bit more than you think might be necessary while you’your gone?


Thanks for the links @JPedrego. I didn’t even know these existed! Do you know if they clog over tune any more or less than the ones that aren’t pressure regulated?


I doubt they do but I have nothing solid to base that on, just my own intuition


@JPedrego Fair enough. Thanks again…


@azdavidr, I’ve got the coefficient set at .95 and it wants to water every day. I’ve changed my emitters to .3in/hr and I’ve got the zones set at 130% to have them put some extra water down that doesn’t go into moisture levels. What I’m getting caught with is that 10-20% chance of rain every afternoon that doesn’t materialize. If I’m home, I keep an eye on things, and I’ve got a fixed schedule set up that I just run manually. But traveling I can’t really do that. I’m starting to think that I would really love to have an option where I could tell the Rachio that if the chance of rain is 20% or less, ignore it and water anyway.

What I still don’t understand is that my lawn is fine, it’s just my drip systems that I run into problems with.


I see. A PWS should help but there’s the expense and overhead of setting one up of course.

I’m guessing it’s due to the higher crop coefficient of weekdays on your drip. The moisture drains much more quickly to they wilting point and gives you less room for error. I have some plants that would suffer with even a single day of error. My Bermuda could care less about a day off missed watering here or there.


Thanks for your comments. I am not sure that I understand your statement: “the only impact the area calculation has is to the water used. With a definition in in nozzles of GPH it would also affect watering duration.” Isn’t the point of using single point emitters that you can regulate precisely the amount of water delivered since you know the volume per time of the emitter and the length of time it is delivered? Where does area come into the equation? There effectively is no area. The whole point of an emitter is that it delivers the water slowly and in a measured format so that the water does not spread out but is soaked up right at the plant. All of Rachio’s calculations are based on sprinkler systems, not emitters. As those of use with emitter systems have found out, their calculations and software is completely useless when it comes to emitters. We can set the watering times manually which is fine, but you can use much less expensive solutions to do that.

I agree that this issue is more complex than it seems but Rachio’s response seems to be to ignore the problem rather than to address it. It would be fine if they would come right out and say that they were uninterested in supporting single point emitters and were really only meant for lawns, but it is incredibly disingenuous for them to say “We are considering the issue and will address it in our next revision.” when they really aren’t. There are several nurseries in my area that either refuse to recommend Rachio or recommend against Rachio for precisely that reason.