Flow meter, Square footage & Nozzle output settings

@naamang, the listed features of the WFM don’t imply controlling flow rates. “Monitor flow rates” and “fine-tune watering accuracy” don’t imply automated adjustments for varying pressure, though that would be nifty and seemingly possible in software. But consider that if pressure induced varying flow rates were accounted for, then leak detection wouldn’t be possible, absent pressure data fed to the unit. One or the other it seems to me.

Also, heads perform wildly different at varying pressure. From distance thrown to misting, which would throw off the theoretical gain from doing a simple gpm/ft^2 calc. I’d stick a pressure regulator on the line into the irrigation system to get consistent head performance first and foremost, which would seemingly eliminate your problem of irregular flow rates. I went with individual pressure regulated bodies with my heads for that reason, and pressure compensated drippers on my drip zone. Given the fully pressure regulated system I now have, the flow meter gives solidly consistent flow rates. My city incoming varies from 110 to 70 psi over the course of the year and it doesn’t matter.

Obviously the meter and setup don’t fit your needs, no argument there. I just don’t think your assessment of dishonesty is accurate.

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Good tip on the pressure regulator but I didn’t say “fine tunes watering accuracy” implied controlling flow rates, I said it implies accurate amounts of water being applied to each zone via on-the-fly watering time adjustments. And if it doesn’t imply this, please tell me what it does imply, because Franz is smart enough not to answer this question.

His words:

Those two features were covered under the first two bullet points of the Know With The Flow selling points. The final (4th) bullet point " * Pair with Rachio 3 to fine-tune watering accuracy" implies that the flow meter works with the controller to apply accurate amounts of water to each zone as needed.

I’m not a software engineer but it seems like a simple fix to make this happen. It already knows, based on weather data, how much water is needed in inches so all it needs to do is figure watering time. To do this, it would simply need to calculate square footage x inches of water per square foot. There is 7.481 gallons in a cubic foot so divided by 12 (inches) = .6234 gallons to apply 1 inch of water to 1 sq.ft. of yard. So if zone 1 is 1000 sq.ft., then it need to apply 623.4 gallons of water to zone 1 then stop.

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You assume that everyone knows the square footage of each of their zones. That will be a challenge for many customers! (I am one of those!)

Yes, I’m assuming most people know how to read a measuring tape and multiply. But, for those that don’t, they could always use the default nozzle output value and be right where EVERYONE is now, simply guessing at it.

@naamang. When I first bought the flow meter, I assumed (like you did) that one of the benefits would be that the flow meter would help the controller regulate the duration of watering by zone (instead of using the fixed value input into the program) to hit a target watering volume (1" or 1.5" per week). However, while that would be awesome, I think it would be quite challenging to implement accurately for all or a majority of customers.

Consider these issues:

  1. Changing input water pressure (city or well)
  2. Variation in soil types within a neighborhood and perhaps even within a yard, which will impact moisture retention/runoff etc. Other users (in other threads) have indicated that in newer developments, soil is trucked in from who knows where, so even the US Forestry Dept data may be inaccurate.
  3. Spray overlap. I know that a few nozzles from different zones in my yard overlap. I tried but it’s hard to estimate how much it is. It could be 50% in one part of the zone and 70% in another, because of the frequency of the overlapping arc from a neighboring nozzle.
  4. Inability to accurately predict precipitation levels. Unless you have a personal weather station that is 100% accurate for 100% of your area being irrigated, there’s bound to be some deviation from what the station says it rained and the actual amount. In my case the nearest weather station is 0.7 miles away, so I’m sure there’s a difference between the actual amount of precipitation and reported.

Oh, I don’t think people in general are as anal about this issue to know the area of their yards. And it’s not related to their ability to do math and measure. It’s just that they trust the installer knows what she/he is doing and will call them if the lawn goes brown.

It sounds like you would like to accurately control the amount of water your yard gets. While that’s a noble goal, for the reasons above (and others that I’m unaware of), it’s unlikely. Unless you have a 1 sq.ft yard of uniform thickness, composition, 0 slope, and you can control other variables like evaporation, wind…

For now, I think the flow meter is good for knowing approximately how much water has been consumed and to calculate the approximate watering times to reach your desired watering levels. Like you mentioned, I used the area, flow rate and a guesstimate of overlap between nozzles of different zones to calculate zone watering time to obtain 1.0" of watering per week.

The biggest benefits of this system IMO are the ability to view what’s going on my phone, tweak things from anywhere (instead of standing in front of the controller) and the potential to benefit from future software upgrades.

Do share with the community here if you do find a solution that can adjust watering days AND duration to a target watering depth. That would be awesome.

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I do agree with naamang that Rachio’s advertising is misleading. I was under the same assumption that the flow meter would be used to measure actual watering rather than based on a fixed flow rate.

@franz What’s really frustrating about this is that it should be easy to add that feature (I am a software engineer). Your offer to “refund the money” is a copout in my opinion - especially considering the hassle of installing - and uninstalling of the flow meter.


How do you figure everyone is guessing at it? I figure you would know how to look up the manufacturer of your sprinkler nozzles and figure out what the PR is…or do a catch cup test to also help you figure out the uniformity.

  1. Changing input water pressure only effects rate of flow. Rate of flow is measured by the flow valve.
  2. The “Variations in soul types" factor is already part of the controller’s configurable settings as "Soil Type” and it’s water retention properties as "Available Water" in advanced settings. This data is already used to regulate watering time.
  3. Spray overlap (throw) is configurable on most impact sprinkler heads via a diffuser screw. A knowledgeable installer will have head placement and throw properly set to achieve uniform coverage. This shouldn’t be an issue if it was installed professionally.
  4. If you read the selling points on the Rachio 3 Smart Controller before you purchased it, you would know it’s equipped with hyperlocal Weather Intelligenc Plus, a technology that uses satellite, radar and weather station data to make automatic weather adjustments based on your location. Here is the exact wording from Rachio:

What is Weather Intelligence™ Plus?

Weather Intelligence™ Plus is an exciting new feature available for Rachio 3 that provides hyper local accuracy into the current and projected weather that’s not only in your area, but right outside your door.

I’m not “anal” about the area of my yard, I’m just wanting the accuracy I was promised when making my purchase and square footage would be part of that equation. And, for reasons unknown, footage is one of the configurable advanced settings in the Rachio app.

It is there for those that don’t have a flow meter to get a decent idea on the actual water usage of the system, in total gallon output.

Everyone is guessing at it because nozzle output varies with water pressure. We’ve already covered that in this discussion. And yes, I could do a rain gauge test but why should I when I already purchased the technology to do the job for me… or at least that was what I was lead to believe.

Most nozzles have less than a 10% variance between 25psi, and 55+psi. Trust me, there are A LOT of other variables that are going to cause problems


This is what I’m doing to make this do what I want. I purchased a Zurn 1-600XL Wilkins Water Pressure Reducing Valve from Amazon and put it inline between the expansion tank and my anti-syphon valve. This will keep the water pressure at 45 psi which will in turn maintain consistent flow. I can now calibrate the flow meter and use the resulting gpm to figure my nozzle output (GPM divided by number of heads in zone). This valve will also make the sprinkler heads more efficient by reducing mist caused by high pressure and will maintain more even coverage due to consistent throw.

Totally agree. The closer you can hold the pressure to the nozzles recommend spec, the better. Curious how your value will differ from what the manufacturer specifies on their nozzle.

@naamang Look, I’m not debating to prove that I’m correct or that you are wrong. In fact, my knowledge of sprinklers/irrigation systems is just about average. I’m a homeowner that is interested in maximizing the efficiency of my home sprinkler system. I agree that the marketing verbiage is somewhat misleading, I was also under the impression that the duration of watering would somehow be regulated by the flow meter. But it doesn’t bother me. What is marketing if it doesn’t include a bit of hyperbole?

However, I’m not sure one can achieve the level of accuracy you seek. BTW, what level of accuracy is sufficient for you? 90%? 95%? All I’m saying is that most installations with typical average nozzles, valves, conduits, etc. will have that much variation.

  1. Are you saying that if the pressure at one nozzle falls by say, 5-10%, the radius/volume of water output will not change? If the throw (radius) changes, then so does amount of water per area, right?
  2. Again, I’m not sure the soil type data I have is correct, unless I have soil tested. I’m assuming its correct. I don’t know if the developer trucked in soil from 10miles away or 50 miles away or not at all. But this is a minor factor.
  3. I understand throw is configurable, but installers don’t use a ruler to determine placement of heads to within a few inches. At least mine didn’t. I have one area of my yard that gets sprayed by nozzles from 3 different zones. These nozzles have different throws. Although calibrated at the factory to be identical, in the 15 years since they were installed, I can see that the spray pattern has changed. But not enough for me to tweak them or worry about changing them. So I cannot determine how much water this one area gets with 100% accuracy. I’d have to probably do a 100 cup catch test for an hour or more to get a reasonable average value.
    3a. So how do I calculate “area”? Its not a rectangle, but a mish-mash of full 360 degree arcs, some 1/2 arcs and some 3/4 arcs. The rotors don’t rotate with exact precision. One seems to be slower than the others. I’m not sure about you, but calculating the area of several overlapping somewhat circular shapes is not easy. In fact, I’d say its a significant challenge.
  4. Agree about “hyper local intelligence…” being misleading. Its their best guesstimate based on data supplied by a 3rd party. That’s their out.
  5. And other factors that I don’t know but can guess (wind, evaporation etc).

Above all, if the flow rate changes between calibration and actual run or during a run, its just not easy to adjust watering time on the fly. I’m sure you appreciate that. The software loop to do that calculation will be complicated and prone to error.

I’m sure these factors contribute to at least 10% deviation from a theoretical calculation. I can live with that. The reasons I’m appreciative Rachio are that it gives me better insight into what is going on, the ability to turn on/off a sprinkler by standing near it and not running back and forth into my garage and the potential that the software can get better. And the software/hardware look pretty modern. There was not another system that seemed to deliver these (subjective) factors, so I went with the system and am pretty satisfied with it.

OTOH, I am confused by what “Flex Daily” actually does. I entered certain watering times for 3 zones when configuring them and I notice they changed for up-coming sessions. So how did the algorithm calculate the changes? If it did it on parameters like % of soil dryness (or whatever the technical term is), surely, to your point, it can calculate amount of water required for a certain area and flow to achieve a watering target. I’m assuming you want to set all the parameters (soil type, slope, sunlight, all the parameters in the “advanced” tab), plus flow rate per zone, set a target watering level, maybe limit days on which to water and presto! the algorithm calculates watering times based on these plus weather intelligence parameters. At least that’s how I would do it. Don’t know what Rachio does. Is there a complete technical explanation somewhere that I missed?

I’m a physicist and engineer with significant software experience (own an app business with a s/w dev team), so feel free to geek out on me.

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How is knowing your square footage going to help you know your water usage? You find your water usage by multiplying your nozzle’s gpm rating at the average pressure of your system by the number of heads in the zone. It’s worthless in the advanced settings if Rachio isn’t going to use it to regulate watering accuracy.

Because, your nozzles put out a PR (in/hour), and the amount of water can be converted to gallons if you know the area being watered. Is it 100% accurate, no. Does it give you a decent snapshot of your usage, yes. Same can be said for the flow meter from Rachio. I don’t know if they publish the accuracy, but you can only expect so much from a $100 flow meter. Hell, your $2000 city water meter is still only accurate to a certain degree…

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My system is on a pressure regulator, and I see very little variation in flow rate run to run, since my trip point is set to the default and it has never alarmed yet.

Therefore, I used the calibration gpm, square footage and an excel spreadsheet to calculate the nozzles inches per hour. As everyone noted this is not rocket science, and excel did the job just fine. I then entered the resulting data into the advanced data for each zone. The calculated nozzle inches/hour were in some cases quite different to the original guesses based on nozzle type, and so now I feel I have improved the accuracy versus just guessing.

Of course this calculation does not take into account all the on the ground variables like nozzle overlap, pattern variation and so on, but only rearranging the nozzles will fix those types of errors, and it will never be perfectly uniform no matter what you do. I am just trying to get close.


I had the same expectation as others that the data from flow meter would be utilized. I have calculated my square feet per zone (which I have and entered in the app)- but I am not sure how the app uses this data. Does this update the nozzle in/hr rate? I don’t see anything in the app to capture how many nozzles there are in a zone. So my question is, I have a flow GPM per zone, I know each zone size. What is the calculation to convert GPM over SQ FT to IN/HR?

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That was my complaint. The flow meter data is useless to the app for anything other than leak detection, and only if you have consistent flow. No it doesn’t update the nozzle output.

This is how I’m calculating my nozzle output now that I’ve got consistent flow via the new valve:

GPM of the zone multiplied by 60 (minutes) = GPH, divided by square footage, then divide that by .6234 (gallons per 1" x 12" x 12" area).

So, for the sake of an easy math example, let’s say your zone’s gpm is 10 and your square footage is 1000. We’ll multiply 10gpm by 60 to get 600gph. Now we’ll divide 600 by 1000 sq.ft. to get .6 gal per sq.ft. Now we’ll divide .6 gal by .6234 gal to get .962 inches per hour nozzle output collectively.

Now, in the real world, my gpm is 9.5 and my square footage is 1427 in Zone #1 so my nozzle output is only .64 inches per hour, way under the default value of 1"

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