It really isn’t that hard, but I know most people want to add all sorts of weird variables to complicate things.
There’s really only 2 things to keep track of:
1. What you did before (“dumb schedule”)
2. What you’re doing now (“smart schedule”)
and the difference is the cost decrease(savings)/increase incurred.
Now, the default setup process can easily create a “dumb schedule”, which would be the same as the “smart schedule”, just without all the sensor input. Why? Because the same schedule could have been entered into a standard irrigation unit, even if the individual zones can different schedules due to all the various factors entered (slope, vegetation, soil type, etc). So the “saved” would be where the smartness comes in, alas where the unit doesn’t turn on the sprinklers due to previous/anticipated precipitation, air humidity, cloud cover, you name it.
For example, in my previous unit i had programmed 4min waterings per zone (slope), 3 iterations (clay soil), 30min wait period (clay soil), where each zone had different number of days due to difference in vegetation and shade. Yes, my unit was dumb, but the schedule was smart, but it could not take into account the other variables, due to the unit I used. But it was pretty darn close to optimal without those factors.
So by following the default, you get the water saved by being a smart unit, but of course, not compared to what you had before, if you had a dumb schedule, on a dumb unit. That’s what I noted as the “super-advanced feature”, where you could input your old schedule to get even more accurate savings model.
So what would it really take? Just have the Rachio create a “virtual” schedule which represents the dumb/previous schedule, and measure on/off differences between the “virtual” and active schedules. Done. Easy.
If you want accurate gallons used, I guess install a Flow Sensor?