Ajax Water Is Hard — Here's What It Costs You Each Year
7.31 GPG · 125 ppm · +12% vs Canadian average · 2025 report
Source: Durham Region (Regional Municipality of Durham), 2025 report
HardAjax water is hard at 7.31 GPG (125 ppm). Scale and spotting are noticeable, and a softener or conditioner is worth considering.
How we calculate this: based on the Battelle Memorial Institute study commissioned by the Water Quality Association (WQA), hard water is estimated to cost the average affected household roughly $800/year in 2010 dollars (~$1,230 today, after ~54% inflation). We scale that by 7.31 GPG versus a ~10 GPG reference. The percentages above come from the Battelle Memorial Institute study (commissioned by WQRF), the US Department of Energy, and the Water Quality Association. This is an estimate — not a certified per-household figure — and actual savings vary by water use, fuel type, and local rates.
Hardness
Parts per million
vs Canadian average
Contaminants in water
How Ajax Compares
Water hardness scale
| Classification | Grains per gallon (GPG) | mg/L (ppm) | What it means |
|---|---|---|---|
| Soft | 0–3.5 | 0–60 | No scale; softener unnecessary. |
| Slightly Hard | 3.5–7 | 60–120 | Minor spotting; conditioning optional. |
| Hard← your water | 7–10.5 | 120–180 | Visible scale; softener recommended. |
| Very Hard | 10.5+ | 180+ | Heavy scale; whole-home softener strongly recommended. |

Why Is Ajax Water So Hard?
Ajax gets its water from Lake Ontario, and the Regional Municipality of Durham treats and distributes it through the Ajax plant. That makes Ajax a surface-water city, plain and simple. There are no deep wells or groundwater aquifers feeding your taps. So the hardness you’re dealing with comes straight from the lake, and the story of why that water is hard starts well before it ever reaches the intake pipe.
Lake Ontario is the last stop in the Great Lakes chain, and by the time water gets there, it has traveled a long way. The lake’s watershed drains a massive area of land that includes limestone, dolomite, and other calcium-and-magnesium-rich bedrock. Rain and snowmelt run over this terrain, and as that water moves through the soil and over the rock, it picks up dissolved minerals. Carbon dioxide in the water makes it slightly acidic, which accelerates the breakdown of carbonate rocks like limestone. That process releases calcium and magnesium ions directly into the water. By the time the water reaches Ajax’s intake, it’s carrying a measurable load of dissolved hardness.
The numbers back this up. Ajax water sits at about 7.31 grains per gallon, or 125 parts per million as calcium carbonate. That puts it right at the threshold the USGS uses to classify water as “hard” (anything above 7 GPG). It’s not off-the-charts hard, but it’s hard enough that you’ll notice it in the shower and on your dishes. The lake acts as a giant mixing bowl, so the hardness level stays fairly consistent year-round. It doesn’t spike after a rainstorm the way some groundwater wells do, but it also doesn’t drop much during wet seasons. What you get is steady, moderate hardness that comes from the geology of the entire Lake Ontario basin, not just the immediate shoreline.
How Ajax Compares to Nearby Cities
If you live in Ajax, your water is essentially the same as what your neighbors in the Durham Region are getting. The Regional Municipality of Durham operates a coordinated water supply system, and the Ajax plant is one piece of that network. Other Durham communities, including Oshawa and Whitby, draw from the same Lake Ontario source and treat it through the same regional system. That means the hardness profile you’re dealing with is very similar across the region. There can be minor variations in treatment blending or seasonal conditions, but the source water is Lake Ontario for all of them.
The bigger contrast comes when you compare Ajax to cities that don’t use the Great Lakes. Many municipalities in southern Ontario rely on groundwater wells that tap into deep limestone aquifers. Those wells often produce water that is considerably harder than Ajax’s lake supply, sometimes pushing well past the 10.5 GPG mark that USGS classifies as “very hard.” So while Ajax water is technically hard, it’s on the milder end of the spectrum compared to some of its inland neighbors. You’re not dealing with the kind of extreme hardness that leaves crusty white buildup on every faucet within a week.
That said, 7.31 GPG is still enough to matter. The EPA doesn’t regulate hardness as a health hazard; it’s purely an aesthetic issue under the Secondary Maximum Contaminant Level guidelines. But the practical effects are real. Based on the WQA-commissioned Battelle Memorial Institute study, hard water is estimated to cost the average affected household more each year in extra energy, premature appliance wear, and additional cleaning products — see the cost calculator on this page for the number scaled to this city’s actual hardness. Battelle Memorial Institute research from 2009 found that gas water heaters lose roughly 4% efficiency for every 5 GPG of hardness, and the Department of Energy notes that just a quarter-inch of scale buildup can cut water heater efficiency by up to 40%. At 7.31 GPG, you’re not in the worst-case scenario, but you’re firmly in the range where scale accumulates and appliances work harder than they should.
How does Ajax stack up against the rest of Ontario? It's hard at 7.31 GPG — Woodstock, Guelph, and Ingersoll sit nearby with different numbers. See the full hardest-water ranking for context.
See where Ajax sits on the Ontario water hardness map →
Want the broader explainer on what hardness actually is and how it behaves? Read hard water vs. soft water, explained.
What 7.31 GPG Actually Does to an Ajax Home
At 7.31 GPG, hard water stops being subtle in a Ajax home. Here's what it actually does:
- Water heater efficiency drop. The US Department of Energy (and its equivalent studies) attribute scale as the single biggest efficiency killer in hard-water homes — at 7.31 GPG, your heater operates roughly 6% below where it would on soft water, which shows up directly on the energy bill.
- Fixture and glassware scale. White mineral deposits build on faucets, showerheads, and dishes within weeks of cleaning.
- More detergent. The Water Quality Association notes hard water can require 50–75% more soap to achieve the same cleaning — and fabrics wear faster from mineral abrasion in the wash cycle.
- Shortened appliance life. Dishwashers, washing machines, and water heaters accumulate internal scale that quietly cuts their service life.
The Battelle Memorial Institute's study — commissioned by the Water Quality Research Foundation — is the cleanest proof: water heaters on untreated hard water failed in under 2 years of the 10-year test, while identical units on softened water ran the full decade. The mineral damage is real and measurable.
Do You Need a Water Softener in Ajax?
Yes, for most homes. At 7.31 GPG, Ajax water is hard enough that a whole-house ion-exchange softener pays for itself — through longer appliance life, less detergent, and less descaling. The Battelle water-heater finding alone (untreated units failing in under 2 years) makes the case at this hardness.
At 7.31 GPG a salt-free conditioner will reduce scale but won't remove the minerals — you'll still get the soap and skin effects. For actual softening, ion exchange (a traditional softener) is what removes hardness.
What Size Softener Does Ajax Need?
Sizing a softener is a two-number equation: your household's daily water use × your hardness. The rule of thumb is grains per day = (people) × (75 gallons) × (GPG).
- At 7.31 GPG, a family of four uses roughly 2,193 grains of hardness per day.
- A 32,000–48,000-grain softener regenerates roughly every 12–18 days — within the 3–7 day window that keeps salt and water use efficient.
- Round up, not down: an undersized unit regenerates too often and wastes salt. Metered (on-demand) regeneration saves the most salt and water.
For Ajax at 7.31 GPG, a 32,000–48,000-grain metered softener is the safe default for a 3–4 person home. A larger household, or one with unusually high water use, should size up to 64,000 grains.
What Are the Signs of Hard Water in a Ajax Home?
At 7.31 GPG (125 ppm), Ajax residents notice significant hard-water effects. The USGS classifies water above 7 GPG as hard and notes it causes measurable physical damage to plumbing and appliances.
- White or grey crust on faucet aerators, showerheads, and around drains — calcium carbonate depositing as water evaporates.
- Spotty glassware even after a full dishwasher cycle — mineral film left behind when water dries.
- Falling water-heater efficiency — scale insulates the heating element, forcing the unit to work harder and pushing up the energy bill.
- Flat, stiff hair — calcium bonds to hair proteins and prevents shampoo from rinsing clean.
- Dry, itchy skin — dissolved minerals disrupt the skin's moisture barrier.
- Weak soap lather — hardness ions react with soap to form insoluble scum instead of suds.
- Shorter appliance life — washing machines, dishwashers, and coffee makers accumulate internal scale.
The Battelle Memorial Institute study commissioned by the Water Quality Research Foundation found untreated very-hard-water heaters failed in under 2 years, versus a full 10 years on softened water. At Ajax's 7.31 GPG, that equipment degradation compounds faster than most homeowners expect.

Best Treatment for Ajax Homes
At 7.31 GPG you want actual removal, not just scale prevention. Two pieces of equipment cover most needs:
Aquasana SimplySoft 40,000-Grain Softener
A metered whole-house salt-based softener sized for Ajax's 7.31 GPG. Removes hardness minerals via ion exchange for genuinely soft water — no more scale, spotting, or stiff laundry. 40,000-grain capacity regenerates about weekly for a typical 3–4 person home.
check current price
See on Aquasana →Aquasana SmartFlow Reverse Osmosis (drinking water)
The under-sink RO handles everything you drink. Removes lead, arsenic, fluoride, mercury, and PFOA/PFOS — then remineralizes for taste. The higher-purity companion to a whole-house softener or filter.
check current price
See on Aquasana →
A whole-house water softener pays for itself in roughly 13 months at Ajax's hardness level — after that, the savings accrue every year.
How Do You Test Water Hardness in Ajax?
This page reports Ajax's system-wide average (7.31 GPG), but your tap can vary slightly by neighborhood, pipe age, and in-home filtration. For a step-by-step, see how to test your water hardness at home — it walks through test strips, the free soap-shake check, TDS meters, titration kits, and certified lab tests.
- Test strips (~$10) give a GPG reading in about 30 seconds and are accurate enough to decide whether to invest in treatment.
- TDS meter (~$15) measures total dissolved solids, a rough hardness proxy — but it doesn't separate hardness from other minerals.
- Lab test — most water treatment companies in Ajax offer free in-home tests (expect a sales pitch); for an independent result, the EPA maintains a list of certified labs.
Note: the EPA doesn't regulate hardness (it's a nuisance, not a health hazard), but the EWG Tap Water Database tracks contaminants above health guidelines for Ajax's utility — see our Ajax water-quality report for what's actually been detected.
What about Ajax water quality?
Hardness is separate from safety. Ajax's water meets all Health Canada legal limits — 1 detected contaminants, none above the limit.
The ones people actually ask about:
Compare Ajax to Other Ontario Cities
Other Hard Water Cities
Explore More
Frequently asked questions
Is Ajax water hard or soft?
Ajax, Ontario water is hard at 7.31 grains per gallon (125 ppm). That is considered hard enough to cause scale buildup and spotting.
How much does hard water cost the average Ajax household?
Based on the WQA-commissioned Battelle Memorial Institute study, hard water is estimated to cost the average affected household roughly $800/year in 2010 dollars (~$1,230 today after ~54% inflation) — an estimate, not a measured per-household figure. Scaled to Ajax's 7.31 GPG hardness, that works out to about $899/year (or ~$74.92/month) for a typical home — see the calculator on this page for the full breakdown.
Does Ajax need a water softener?
Likely — at 7.31 GPG you'll see spotting and scale, and a softener or salt-free conditioner will help.
Why is Ajax's water hard?
Hardness comes from the geology of Ajax's water source. Lake Ontario (Durham Region water supply — Ajax plant) dissolves calcium and magnesium as water moves through the ground, and those dissolved minerals are what "hard water" means.
How do I test my water hardness in Ajax?
Use a home test kit (test strips for a quick read, or a TDS meter for dissolved solids), or check your utility's annual Consumer Confidence Report (CCR). For lab-accurate results, send a sample to a certified lab.
Who supplies Ajax's water?
Ajax water is supplied by Durham Region (Regional Municipality of Durham). Its annual water quality report (Consumer Confidence Report) is the authoritative source for local hardness and contaminant levels.
What's the difference between grains per gallon and ppm?
1 GPG (grains per gallon) equals 17.1 ppm (mg/L). To convert: 7.31 GPG × 17.1 = ~125 ppm. Water is "hard" above roughly 7 GPG (120 ppm).
Sources & data
Hardness and water-quality data compiled from authoritative public sources.
- Durham Region (Regional Municipality of Durham) — primary hardness/water-quality source
- Durham Region (Regional Municipality of Durham) — annual water quality report (CCR)
- Health Canada — Guidelines for Canadian Drinking Water Quality
- Government of Canada — Water quality
- USGS — Water Hardness
- Water Quality Association — Scale & Hardness
- EPA — Drinking Water Regulations
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