Need parameters for filling pools, ponds, fountains, etc

Hi everyone.

I have a 16 zone Rachio 3rd gen, and need help setting up autofill for a pool and a fountain.

I asked about this a few years ago in the forums, but it seems no new info has really come out that I could find.

Seems like a body of water with no vegetation should have some specific parameters that are different, and possibly more basic, than a yard or garden.

Can someone from Rachio, or perhaps a user with advanced understanding, help determine what would be a good starting parameter for a pool, fountain or pond? I think I can figure out the fill rate, but need help getting it the calculate evaporative rates to some reasonable accuracy.

Thanks in advance.

Evaporation off of plans is driven by photosynthesis and is much different compared to water surface evaporation off of the pool. Unfortunately there are no settings you could tweak in order to better match your pool losses. Should you fill you pool based on math alone, you’ll quickly find that even a 1% error will cause your water levels to drop below the operating range of the pool or, worse yet, overflow.

In order to even start accounting for your pool losses, you’d need to monitor and account to temperature difference between the water surface and the air, not to mention relative humidity, pool chemistry, sun exposure / shade coverage, pool use, etc… None of this data is available to Rachio and their code is not designed for such use case. Pure water loss to air is not really a thing with soil, which quickly absorbs the water below the surface, whereas it mostly goes on to precipitate down to ground water and make it’s way back into the water cycle via springs.

Some members went on to connect their water level valves to an irrigation zone, which allows them to schedule the time the water can be added to the pool, though the amount is still controlled via traditional means. This primarily has a benefit of preventing a small 24/7 leak from causing high water bills.

I know this is not the answer you were looing for, but it’s an unavoidable fact that an irrigation controller, no matter how smart, is not well suited as a purely predictive pool refill device.

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I’ve been using the Rachio for about 10 months to refill the pool.

I have it under estimating, so it doesn’t overflow.

Then I can trigger it via Alexa or the Rachio app, to top off manually.

It mostly works great. I was just wondering if there was anything more accurate than what I’m already doing.

In case it helps anyone else, I have the following settings…

Zone Type: Warm season grass
Spray Head: Rotor (I customized flow under Advanced)
Soil Type: Sand
Exposure: Lots of Sun
Slope: Flat

Advanced Settings…
Area: area of my pool
Available Water: 1 in/in
Root Depth: 6 in (I think I need to narrow this to more like 3 or 4 inches, however much pool varies)
Allowed Depletion: 50% (if I reduce root depth, I can probably increase allowed depletion)
Efficiency: 100% (guessing on this)
Crop Efficiency: 100% (guessing here too)
Nozzle Inches Per Hour: 4 in (I think this is pretty close to mine, but I recommend over estimating this so it fills for a shorter time and doesn’t overflow)

My Pool Fill Schedule is set as follows…
Type: Flex Daily
Interval: (every day enabled, but you can do specific days only, if you want)
Zones: (my swimming pool zone)
Watering Duration: (mine works out to about 19 m, about every week or so)
Time: I have it go at sunset, just so I’m usually available to see it if something goes wrong
Cycle and Soak: None/Off
Weather Intelligence: Freeze Skip On, Wind Skip Off (probably not important either way)

Hope it helps.

If anyone has something better, let me know.

I’m glad it works for you, but others should keep in mind that settings that work for @Tyber, may not work for you. correlation ≠ causation. Start small, experiment, but keep in mind that seasons will likely change the established balance.


I don’t doubt it. I suggested something similar to what you’re doing some time ago using Flex Daily.

It’s Crop Coefficient, and I think 100% is perfect, as it uses the 100% of the FRET value which is defined as evaporation from an open pan on the ground.

This is pretty important IMHO, but you should be able to measure it by taking the gallons per hour and the area of the pool into account.

Your Crop Coefficient, recommended at 100%, and the local weather will determine how much water is required per week, and is the most important value. Root Depth, Soil Available Water and Allowed Depletion only determine how much water is applied at one time. Which in turn affects how often it waters (okay, Fills). If you’re happy with how often it fills, leave all those settings alone. If you want it to fill more often (with less water) decrease any one of them. The opposite to fill less often.

IMHO, the only thing that this doesn’t take into effect is loss of water from splashing or excessive wind, or leakage. I see no reason why it shouldn’t work well for you. But your idea of keeping the flow on the low side, and accepting that nothing is perfect so you may need to do a manual add now and then, sounds great. The problem with yards is really not really any easier, yet people expect to go years without looking at anything.