Well water


We have two options at our residents: buy city water for $16/kgal, or use well water. City inspector estimates a consumption of 40-45kgal for irrigation per month (hot TX sun). The well yields 5 GPM, the zones measure 15-30 GPM.

One solution would be to pump into a buffer 500 gal tank, and then run a single zone, then wait until the tank is full again, and run the next. There are 24 zones.

These are options:

a) A sensor input that tells the controller to wait until the tank is full before to start the next zone. Only run one zone, then check for “full”.

b) A timer, that has a hold-down of one hour in-between zone calls.

c) A sensor that reports fill-level to the controller and calculates zones calls appropriately.

d) Keeping track of fill-level via flow sensor. Not as precise, needs an error margin.

We can theoretically water 24/7. However, it is advisable to leave the hottest portion out of the day. Hence, we may water a few zones one day and another the next. The complexity is of course also the weather. If it is raining, we skip that zone, or future zones, and how much watering do we make up for.

Which options sound feasible with Rachio?


@sbrunner - this is current as of V2.x of Rachio, V3.x may change things.

  1. The largest controller is currently 16 stations, so at least two controllers would be need.
  2. Each controller would need to be scheduled separately (e.g. one for M, W, F and the other one for S,T,Th or one from 3 AM to 9 AM and the other from 6 PM to Midnight - every day) as one currently can’t schedule across or combine controllers.
  3. There is no well delay in the current software - this has been/is a very frequent request. So right now the solution is to add a phantom zone that is not hooked up to anything between actual zones to act as a well delay. This would require three Rachios to enable the every other zone is a real zone configuration.
  4. I would hook the low water/tank empty sensor up to the Rachios sensor port as a Rain Sensor so that the Rachios won’t continue to think they’re watering when the pump from the tank isn’t providing water. If one is using a Flex schedule (probably won’t matter for the Fixed time schedule) this should help keep the available water level correct.

Or as Brody might say - You’re going to need a bigger tank.


I thought about the rain sensor port. But I am not sure how this port has been implemented. I would think, typically, the rain sensor does not delay the execution of the next current and next zones, but instead interrupts the current watering cycle.


Also, how to you connect a sensor, such as a flow sensor, to two Rachio controllers?


@sbrunner - correct, the rain sensor won’t delay the execution of the zone, but it will keep the available water balance correct, so the Rachio would fire again on the next schedule opportunity. See this post -> ‘Freeze Protection’ at 50 Degrees (F) Implemented around using the sensor port to prevent watering at freezing temperature, but keep the available water value correct.

The flow sensor is to help provide Rachio with accurate usage versus square feet times precipitation rate times time. If both Rachios are watering at the same time the flow would be double counted. I think due to common wires one would need to either use two flow meters, one for each Rachio, or use an isolator to isolate the commons from each other.


How would an isolator look? Simply two diodes?


@sbrunner, I have no idea if this would work on not.

Here is an article about shared common wires -> https://support.rachio.com/hc/en-us/articles/115010542808-How-do-I-wire-one-master-valve-pump-or-common-wire-to-two-controllers-

And I think on the Sensor Ports the common is actually not the SC port. There are other posts about that.


As long as the schedule is a Flex Daily (fully automatic), the ‘Rain Sensor’ port would work well.

Best regards,



No matter what controller you install, a well with an output of only 5 gallons per minute is really low. If this system is already installed and the zones at 15-30 gallons per minute, the heads will not even pop up. Lets say you have a zone with a 15 gallon per minute demand. The zone has spray heads that run for 12 minutes. 12 minutes x 15 gallons per minute= 180 gallons. If you have a reserve/buffer tank this would work
With just the well, the system will not work. But for a rotor zone with a 30 gallon per minute demand, it becomes more difficult. If you were to operate at 30 gallons per 30 minutes that is 900 gallons. It would take three hours to fill a 900 gallon tank. This is a situation of mathematics.
The utility forbids a cross connection between the well water and the city water.
One idea would be to have 2 entirely separated systems. Use your well for spray and drip irrigation. Use the system from the city to irrigate large turf areas. Limit watering because the rate is do high. You might weigh the cost of having a sprinkler meter so you do not pay sewer charge. You have a high water rate problem and the issue of a low producing well. Do not forget to factor electricity cost for the well pump, cost of a tank.


Yes, 5 GPM is really low. We are probably doing a 500 gallon buffer tank and run one zone at a time, and wait an hour and a half for the tank to fill up again. Cross connections are permissible. Regardless whether you cross connect or not, you need an RPZ backflow preventer, which is a more fail prove version of a double check valve normally used for sprinkler systems. Sewer is metered in the three winter months, not an issue for irrigation. $16 kgal for water compares to electricity cost of about 35 cents to pump. Drip irrigation is extremely expensive to put in, and life expectancy for turf varies. Water demand is determined by turf, which is determined by HOA. Rest of property is drought resistant landscaping.


Per the International plumbing code and the American Backflow Association well water cannot be connected to a municipal water supply because of the high hazard potential of contamination from the well water and the irrigation system.


To decrease the gallons per minute on the spray zones, you could decrease the gpm by 33 percent by using Toro Precision nozzles, available in male and female thread. I have them and really like them.


Youtube: https://youtu.be/v66PIW6GPRw


This is only partially correct. An approved backflow prevention device has to be installed in order to connect well water and city water to the same plumbing system. Per City of Austin code, this device needs to be an RPZ, which is essentially a double-check valve that fails open to drain. Since our well water has high salinity, mixing well and City water is not uncommon.


Yes, the question is what is more cost effective, adding a buffer tank, or redesigning zones.


A licensed plumber is the only one who can tap the city service line. Texas has very strict backflow laws and Austin can only meet or exceed backflow protection. Here in Oklahoma City it is violation to connect well water to potable water.

Austin rules against connection of well to city: http://www.austintexas.gov/department/auxiliary-water-sources

TCEQ: https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.tceq.texas.gov/drinkingwater/cross-connection&ved=2ahUKEwjP8snRy_TYAhUE5GMKHYkdA70QFjAEegQIBxAB&usg=AOvVaw0krM7lryr5axHe-33rGSuw


@sbrunner The RPZ is installed on the city’s potable water side, right? Do they ask for one from the well too?


The link about auxiliary water sources is about cross connection contamination, not about that you cannot have the systems connected.

“Make sure that the public water system is adequately protected by approved and regularly-maintained backflow prevention assembly(ies) at water service meter(s) to any site using an auxiliary water system.”


Table 603.5 tells you what kind of backflow prevention you need for the various cross connects.

I met with Austin Water, and according to them you always need one RPZ directly behind the meter, regardless whether the well is connected or not, just in case somebody does connect it. An “air gap” is only permissible for a rain water collection system. The typical configuration would be: utility shutoff, meter, customer shutoff, PRV, RPZ. If the well is connected and feeds an irrigation system, Austin Water also requested a second RPZ between the irrigation and the potable water, behind the first RPZ, instead of the double check. The RPZ is mounted one foot above the highest sprinkler head. However, you see them typically mounted next to the meter. Not all well owners I know have the second RPZ, and passed inspection anyway. I asked about this, and they said that health hazards are more strictly enforced, and an existing double check may be seen as “prior existing”. Supply pressure in our neighborhood is 150 PSI, hence it would be very unlikely that a well pump could backflow. This is generally about minimizing risk and I think the large concern is bacterial contamination. RPZs and DCs are very similar devices, only that the RPZ has a “reduced pressure zone” between the two check valves. In case of a double failure of these valves, a third drains to ground. If RPZs fail, they typically fail very dramatically with full supply pressure. You do not want to mount one in a basement.

Austin Water did not ask for an RPZ on the well itself. The drawings I saw have typically a plain check valve close to the pitless, or house entrance. There are also a couple of check valves in the riser itself, every 200 feet or so.

You do not have to be a licensed plumber to do the job. The homeowner can also do it.


This scares me when I think about homeowners making service line connections. My point in all of this is to bring attention to the hazard of backflow.
I am thankful that you did your due diligence and asked your utility for information. Many homeowners would never do the right thing. Texas is gradually phasing out double checks as an approved backflow device.


With the number of delays you need between zones, you may have to put zones on separate schedules starting an hour apart each. Using dead zones in the schedule won’t supply enough zones and may throw off calculated water use.

Having well water flow into your house would be just as bad as it flowing into the muni system.

Our weekend house is on a tank. $70/kgal. No landscape gets watered there, lol.