Precipitation Rate Software Suggestion


Since both Rachio employees and users are creating external calculators such as the Rachio Precipitation Rate Calculator and a [Spreadsheet Calculator] (Drip Emitter Calculator for Precipitation Rate & Area) created by @azdavidr, I’d suggest an improvement to Rachio software for drip systems only. Precipitation rate for a custom drip nozzle seems like the wrong input variable since this depends not only on the GPH of the nozzle itself but also on the layout of drip emitters in the zone. It is therefore not possible to specify an accurate precipitation rate by looking solely at the specs of the nozzle. The software would be less confusing if users could enter GPH for a custom nozzle, and also for each zone independently specify watering square footage per emitter (one square foot per emitter could be the default). Otherwise, even if users have exactly the same model emitter throughout the yard, “precipitation rate” for those emitters could be different depending on how much area needs to be covered per dripper.


I know @azdavidr has already demonstrated a nice understanding the solution space in other posts, so I’ll try to provide a slightly different perspective in case I can add any value as a software engineer that works on user interfaces.

Suggested UI Changes

  • Custom nozzles: Provide a way to enter a special drip emitter nozzle type that takes GPH
  • Zones: When the drip emitter nozzle type is used, add the following inputs to the zone:
  1. Average plant canopy size
  2. Average number of emitters per plant

Suggested Business Logic Changes

Internal calculations could still arrive at inches per hour via lookup tables. The lookup tables would depend on soil type and plant type (both are already Rachio zone inputs) and would provide the number of gallons per plant as does Table C in the Water Use it Wisely article @azdavidr mentioned. That article’s tables are probably specific to Arizona soil which is why the article stipulates, “The amount of water needed will vary depending on soil type and soil conditions.” Given the lookup tables and the new UI inputs the software can calculate inches per hour as it does now - no further changes required and backwards compatibility is achieved since the changes are simply extensions of what is already there.

I feel like these changes would provide the simplest way for users to enter a “true” drip nozzle spec that doesn’t change as a function of soil type, number of emitters per plant, etc. as precipitation rate can. Turf and everything else can stay the same and thanks for the great UI, Rachio.


Love the idea @ldslaron . It seems to me the biggest challenge is as you state, that what I outlined is Arizona specific. If there is a way to adapt the necessary “Water Use It Wisely” data to other regions, the method you suggests seems like a “front end” type of a solution, keeping cute algorithms intact. Of course I’m not a Rachio guy so I could be mistaken. I certainly agree entering parameters like number of emitters and cannot size for drop are much easier for a user to grasp that inches per hour for drip!


Thanks, @azdavidr. I put together a Google Docs Sheet that can be used as a playground. I haven’t tested it much yet but maybe see what you think. If you enter 1 square foot (i.e. 1.1284’ canopy diameter), 1 GPH, and 1 emitter per plant, you’ll get the same 1.6042 inches/hour that the Rachio Precipitation Rate Calculator does when you enter 1 gallon in 60 minutes. I interpolated the “Water It Wisely” table to come up with estimated hours to wet the root zone, but that doesn’t drive the precipitation rate directly.


I really like the way you interpolated the “Water Use It Wisely” table @ldslaron, and built it into the pulldown menu! How good of a curve fit did you get ? I suppose the same could be done with the calculator I built but I’d need to add the step of the user inputting the ‘Inches of Water’ number ? Very cool!


Appreciate the compliments, @azdavidr. I didn’t really evaluate the error in the curve fit: I’m sure a quadratic fit would have been better than piecewise linear since gallons should go up with the square of the diameter.

One thing I learned is that precipitation rate can probably be calculated independent of the “Water Use It Wisely” table provided we assume that the system’s drip emitters are able to effectively cover the canopy area. In an extreme example, with sandy soil, a single emitter, and a huge tree canopy, we could provide the number of gallons the tree “wanted” per the table but we might have trouble wetting outside a small cross-sectional area. Lots of water would go down instead of out, leaving much of the root zone dry. It would be cool to see what a computerized 3D soil simulation like Hydrus would predict, but also much more complicated than our spreadsheets (and no longer free).


Good stuff @ldslaron . I agree with what you’re saying across the board. You hit on a challenge that I think is a big one for Rachio. The Flex schedules are very powerful but just a few variables, # of emitters and soil type in your example, can have a big impact. Drip probably complicates things further. Thanks for sharing your ideas!


I corrected the precipitation rate in my spreadsheet and made it dependent on a few more Rachio inputs.