How accurate is your flow sensor reported data?

I did a comparison of my Utility company’s water meter reading with the flow sensor fed data reported by Rachio. There is a 7% difference, which seems rather high. I’d like to share my data and see if the rest of you might be able to post your data for comparison.

My flow sensor is a CST FSI-T10-001.
When a zone with a few rotary sprinklers is run for 5 minutes, my water company meter measures 41.07 gallons. Rachio reports usage of 44 gallons.

I’m wondering if 7% is within the tolerance of the flow-sensor + rachio integration. For a sensor that costs almost $300, I expected more accuracy than 7% difference. Could the water company’s meter be off? I don’t know. I’m curious to learn about the Rachio community’s experiences.


@Waterboy – great questions, I’m hoping other community members will comment on their experience with flow sensor accuracy. Until then, it might be worth checking your sensor installation. Not sure if you’ve reviewed this FAQ from CST, but #6 & #8 have some details worth double checking.


I’ll check tonight, is the app exposing this info yet or do I need to fetch it via the rest interface.

I have the same sensor

Also that 3 gallon difference is right in love be with an old style toilet flush, newer are at 1.5, could that have happened?

Thanks, Emil. Everything installed per spec and water should be full in the pipe.

Hi Plainsane,
No other water used during testing. Tests were run multiple times.

So the last thing that I think could impact this, (I’ll run my own test) is if the sensor measures the leaching after the zone cuts off, not sure, but I could see the gurgle of the water free spinning the impeller if your system siphons after the zone cuts off, and the unit continues to measure inputs after the cycle

Well, another thing that my email communication with brought up was the accuracy of the utility company’s water meter itself. I also did some googling and found several articles about deterioration of water meters over time. Our house is 60+ years old and I don’t remember anyone changing the water meter in the past 15+ years we have lived there. It is quite possible that the discrepancy is caused by a deteriorated utility company meter.

This weekend, I’ll calibrate my utility company’s water meter by filling some reference 5 gallon containers. Let’s see how that goes.

In the meantime, is also contacting CST to see what might be causing the discrepancy.


@plainsane Our measurements stop as soon as the run completes so it shouldn’t be related to any flow before or after. I’m curious to hear what other folks are measuring. We have quite a few beta testers on our list, so I may send a request to see what others measure. Also @Waterboy, be careful with those 5 gallon containers. I’ve been burned by the home depot containers not actually being 5 gallons. I do think there are good ones out there with a line at 5 gallons.

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Dang, was hoping that leak detection,would be possible

I’ll try mine this weekend. Work is so busy I just don’t have any time

@Waterboy I had a conversation with the folks at CST and it’s fairly safe to say that our system accuracy should be within 3%. There may be higher error on short test runs, so make sure to measure on a longer run like your system would use (at least 10 mintues or so). If I were you, I probably wouldn’t report to your utility that your meter may be under-reporting :wink:

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