What hard water does to the ice maker.
Phoenix reported 10 to 17.6 grains per gallon in 2025; Mesa runs as high as 22 and Chandler averages 16.5. A built-in ice machine makes clear ice by freezing water in thin layers and washing away what it rejects, and in water like this, what it rejects is a great deal of mineral. From the kitchen it shows as cubes that turn smaller, then cloudy, then hollow, and less ice in the bin. That is not a fault. It becomes one when the cleaning that the makers actually specify never happens.
What the Cities Publish
Hardness is not a health standard and none of these utilities treat for it, so each one simply publishes the number. Grains per gallon is the unit an appliance manual uses; to convert from milligrams per liter, divide by 17.1.
| Where | Grains per gallon | As the utility puts it | Source |
|---|---|---|---|
| Phoenix | 10–17.6 | 172–302 ppm across the distribution system | City of Phoenix, 2025 Water Quality Report |
| Scottsdale: south of Indian School Road | 13–15 | 230–260 ppm | City of Scottsdale, 2026 Water Quality Report |
| Scottsdale: Indian School to Chaparral | 13–17 | 215–285 ppm | City of Scottsdale, 2026 Water Quality Report |
| Scottsdale: north of Chaparral Road | 13–17 | 230–290 ppm | City of Scottsdale, 2026 Water Quality Report |
| Mesa | 12–22 | “depending on the water source that serves your area” | City of Mesa, water quality |
| Chandler | 5–20, average 16.5 | the average is the figure the city leads with | City of Chandler, Water Quality FAQs |
| Gilbert | average 8–10 | the softest of the five | Town of Gilbert, Public Works |
Paradise Valley has four water providers by the Town’s own list: Berneil Water Company, EPCOR, and the City of Phoenix and City of Scottsdale water services, so an address there may fall under the Phoenix or Scottsdale figures above, or under a provider this table does not cover. Fountain Hills, Cave Creek and Carefree are served by providers other than the city water departments above, and we have no published figure for them. The number for your address is in the annual water quality report your own provider sends.
Why an ice machine minds, and a freezer doesn’t.
A freezer’s ice maker meets your water too, but it freezes the water whole, minerals and all. Cubes from a freezer tray are cloudy because the water freezes all at once and traps air and dissolved minerals in the middle; a built-in machine freezes in thin layers on a chilled surface and washes what it rejects away as it goes. That rejection is the whole reason the ice is clear, and the harder the water, the more there is to reject on every single cycle.
So the same machine, installed identically, reaches the point where it needs attention sooner in Chandler at an average of 16.5 grains than in Gilbert at an average of 8 to 10. Nothing is broken in either one. One of them simply arrives at the maintenance interval first.
What it looks like from the kitchen is a slow slide rather than a failure: cubes get smaller, then cloudier, then hollow; production falls off; the ice starts to taste of the bin. A thickness sensor reading through a film of mineral stops the harvest at the wrong moment, and a fill valve coated with scale on the inside passes less water than the cycle expects. Every one of those reads as “the ice maker is broken”, and none of them is.
What Sub-Zero Actually Instructs
- 01
Clean and sanitize every six months
On an undercounter ice maker, every surface that meets the water system is cleaned and sanitized, and Sub-Zero says that interval stands regardless of the water filtration system used.
- 02
Use the cleaner made for the machine
The solution is what removes limescale, calcium buildup from hard water and other mineral deposits. Sub-Zero does not recommend any other cleaner or sanitizer, including bleach; vinegar only as a last resort, and only on the interior.
- 03
If it will not hold six months, test the water
Sub-Zero’s own answer to a machine that needs cleaning more often is to have the water quality tested and treated, not to clean it more often forever.
- 04
Change the filter every six months, or sooner
On the UC-15I, Sub-Zero says to replace the water filter every six months, after a prolonged shutdown, or when the red REPLACE FILTER light illuminates, and to discard the first batch of ice after a change. A fresh filter does not remove scale that has already formed, which is why it does not replace the six-month clean. The refrigerator cartridge runs on its own two triggers.
Maintenance, not a repair.
Descaling is housekeeping. It is on the list above because Sub-Zero puts it in the owner’s hands, and because we would rather tell you to run the cleaner than take $119 to find limescale.
It becomes our work when cleaning does not bring it back: a fill valve passing too little water, a thickness sensor that has drifted out of adjustment, a pump or a drain that no longer clears between cycles, or a sealed-system fault behind it all. What each of those parts is and how it fails is on the parts page.
One test helps before anyone drives out, on a refrigerator that has both: if its water dispenser still runs normally, water is reaching the unit and the ice maker’s fault is inside the machine. An undercounter ice machine has its own supply line and shut-off valve; check that the valve is open.
Hard Water Questions
How hard is the water where I live?
The city publishes it. Phoenix reported 10 to 17.6 grains per gallon across its distribution system in 2025, Scottsdale 13 to 17 depending on which side of Indian School and Chaparral Roads you are on, Mesa 12 to 22 depending on the source serving your area, Chandler an average of 16.5 against a range of 5 to 20, and Gilbert an average of 8 to 10, the softest of the five.
My ice went small and cloudy. Is the machine broken?
Not necessarily, and this is the one fix worth trying yourself before calling anyone. Sub-Zero says to clean and sanitize an undercounter ice maker every six months whatever filtration is fitted, using the cleaner made for it, and that the solution is what removes limescale and calcium buildup from hard water. If the ice is still small or cloudy after a proper clean and a fresh filter, the fault is inside the machine rather than in the water.
Does a water softener solve it?
It changes what arrives at the machine, and it has a trade-off the City of Mesa states plainly: sodium in softened water rises by about 8 milligrams per liter for every grain of hardness removed. It does not change the maintenance either way: Sub-Zero’s instruction is to clean and sanitize every six months regardless of the water filtration system used.
How often does the water filter need changing?
On its UC-15I undercounter ice maker, Sub-Zero says to replace the filter every six months, after a prolonged shutdown, or when the red REPLACE FILTER light illuminates, and to discard the first batch of ice after a change. The filter and the cleaning are separate jobs: a fresh filter does not remove scale that has already formed, which is why the six-month clean stands whatever filter is fitted. A refrigerator’s own filter runs on different triggers: the indicator in the display, or about one year.
When is it a repair rather than cleaning?
When cleaning does not bring it back. A fill valve passing too little water, a thickness sensor that has drifted, a pump or drain that no longer clears between cycles, or a sealed-system fault are all repairs. We would rather tell you to run the cleaner than sell you a visit that finds limescale.
Sources
- City of Phoenix, 2025 Water Quality Report: total hardness 172–302 ppm, 10–17.6 grains per gallon, from the distribution system table.
- City of Scottsdale, 2026 Water Quality Report: approximate hardness levels by boundary: south of Indian School Road, Indian School to Chaparral, north of Chaparral.
- City of Mesa, common water quality concerns: 12 to 22 grains per gallon depending on the source serving the area, and the sodium added by softening.
- City of Chandler, water quality FAQs: 5 to 20 grains per gallon, average 16.5.
- Town of Gilbert, Public Works water FAQ: average hardness 8 to 10 grains per gallon.
- Town of Paradise Valley, water companies: four water providers, Berneil Water Company, the City of Phoenix and City of Scottsdale water services, and EPCOR.
- Sub-Zero, undercounter ice maker cleaning: the six-month interval, the cleaner, bleach and vinegar, and testing the water when the interval will not hold.
- Sub-Zero, UC-15I undercounter ice maker water filter: replace every six months, after a prolonged shutdown, or when the red REPLACE FILTER light illuminates, and discard the first batch of ice after a change.
- Sub-Zero, water filter replacement: a refrigerator’s filter is replaced when the indicator appears in the display, or after approximately one year.
Written from these sources and reviewed on (checked again ) by Aphelion Appliance Repair, Phoenix. Utilities republish these figures every year and they move; the report for the current year is on each provider’s own site. Cleaning intervals and cleaners differ by model; the use and care guide for yours is the one that counts.
Read Next
- Sub-Zero ice maker: no ice, or not enough?Sub-Zero’s own production rates and the seven checks before anyone is called.
- What a Phoenix summer asks of a refrigeratorRoom heat, condenser dust and monsoon outages, and five checks before you call.
- Chandler ice makers, and the water they drinkThe same numbers, for the city that averages 16.5 grains.
- Water dispenser not working, slow or dryAir after a new filter, a lock, Sabbath Mode, a clogged filter or low pressure: Sub-Zero’s and Monogram’s own checks, down to how long to hold the button.
- An undercounter ice machine that leaks, rattles or stopsWater that is normal inside, thin or clumped ice, the lights by model, and a bin that will not restart.
Cleaned it, and still no ice?
Tell us the make and what the cubes look like. We answer every day, 7am–6pm.