This causes me to pause and wonder if, once you get above 3/8" or 1/2" copper pipe diameters, it could be challenging to install flow sensors that have enough resolution to be meaningful for drip zones.
In my case a flow sensor for my sprinkler system would have to be appropriate for a 1" copper line (leading into the sprinkler water meter) or > 1" PVC line (coming out of the water meter).
Here's an example of inexpensive flow measurement at near drip zone rates, that I did a few years ago. This is accurate measurement of water flow in a 5/8" copper line.
Near the bottom of the picture (before the charts), on the left side, under 'Yesterday,' you can see that 99.3 gals was measured during on times accumulating to 4.1 hours for yesterday's 24 hour period.
That's a measurement of 24 gals/hr rate, or, stated in minutes, a measurement of 0.40 gals/min.
I'm unclear what Rachio Gen 2's plans are for its flow sensor interface - industry standard flow sensors produce a pulse count whose frequency varies as a function of flow.
Today I'm measuring flow for my Iro Gen 2 controlled sprinkler system via reading the on/off times from the master valve. This gives to me this chart:
http://www.welserver.com/perl/plot/WEL0343/Sprinkler1.png (daily usage) and this chart:
http://www.welserver.com/perl/plot/WEL0343/Sprinkler2.png (monthly usage) in hours format. To convert to gallons I too need to add a flow sensor.
My vision of what a Rachio Gen X controller would look like would include support for industry standard flow sensors, accommodation of an Ethernet connection, have a capacity greater than 16 zones (for full automatic operation), and offer a remote zone on/off accessory (that's not an expensive phone.)