Estimate daily irrigation cost using utility bill and rachio gallons reported


#1

Others have described how to use the water meter to determine actual usage. Here is another way to get a course estimate using my utility bill, resulting into gallons and dollars picture, starting with the rainfall and irrigation pattern.


Rainfall is shown in blue using the left Y-axis, irrigation in 1000 gallons in using the right axis.
I am running FLEX DAILY with SMART CYCLE, and you can see we had a rainy period followed by a dry spell with mid 90 temperatures. The rainfall data is coming from the RDU airport WU (1.6 miles away) and a private WU station in our development. They track very well with my local observation. There are some “irregularities” in the irrigation schedule, as I am still experimenting in the face of daily rain promises with nothing leaking from the skies (and on the flip side, there were two days early on where rachio irrigated at 2am and we had a solid afternoon thunderstorm, which on the graph looks like irrigation when it rains).

This irrigation picture translates into the following gallons and dollars picture:

This graph reflects the daily (blue) and cumulative (red) irrigation cost. Here is how I got here:
STEP 1
According to my utility bill, my household base load is 1683 gallons/month without irrigation (average 241 days billing cycles Oct-May)

STEP 2
Utility billed me 12 CCF for last cycle (8976 gal), less base load above leaves me with 7293 gallons irrigated.
The ratio between what ratio reported for the same billing cycle (11193 gallons) and the 7293 billed gallons is 0.651582.
Using the rachio WATERING HISTORY data I multiply all rachio quantities with my .651 factor and get a somewhat calibrated real water usage. (Note: this ain’t perfectly accurate after 1 month, since the utility company only bills in full CCF’s, so on 10 CCF’s there is a 10% error bar).

STEP 3
My baseload of 2 CCF of course covers the “cheap” water. Irrigation goes into the higher price tiers. All in all, I am ending up with about $10 per CCF (simply dividing the water bill with all the water related charges by the CCF’s billed).
Again there is of course a slight underreporting error in there, as I am too lazy to untangle all the tiered additional charges and just used the totals.

CONCLUSIONS:

  • I am impressed with the FLEX schedules, and will keep finetuning parameters, so I don’t have to EMPTY certain zones to get them enough irrigation.
  • It was great while I was out of town (June 27 - July 11), never irrigating and not having to worry and finding everything in perfect shape when coming back.The moisture reporting details were great, and I must say my daily tracking of the WU weather stations gave me comfort that the rain actually fell. Same when I was gone July 23-27 with no rain and the necessity to irrigate some zones frequently.
  • My settings have a tendency to be on the low watering side, but that is where I like them to be, as I can always add water when needed
  • When it is dry and hot, it costs you (see my July 29 additional soak for about $30), but I kind of knew that…

This is a lot of fun - thanks for a great tool!


Total Cost of operation/ownership