Heavy limescale and mineral buildup on a London faucet — 10–13 gpg very hard water
This is what 10–13 gpg does to faucets and fixtures in London homes. Scale accumulates rapidly without treatment.
Quick Answer: London water is Very Hard, averaging 10–13 gpg (171–222 ppm). That is above the US national average of ~10 gpg. London draws from Lake Huron (via Thames River system) + local groundwater. Yes — strongly recommended. At 10–13 gpg, scale accumulates rapidly. A salt-based ion-exchange softener sized at 40,000–48,000 grains is appropriate for most London families of four.

London Water Hardness at a Glance

London, ON — Water Hardness Data

Hardness Range10–13 gpg (171–222 ppm)
ClassificationVery Hard
US National Average~10 gpg (171 ppm)
Primary Water SourceLake Huron (via Thames River system) + local groundwater
Water ProviderCity of London Environmental and Engineering Services
Softener Recommended?Yes — strongly
Hardness Scale Position
Soft (0–3.5)Moderate (3.5–7)Hard (7–10.5)Very Hard (10.5+)

This city's hardness sits near the top of the national scale.

Why Is London Water So Hard?

London draws from Lake Huron via the Thames River system and local groundwater — both of which interact with the limestone and dolostone bedrock of southwestern Ontario. Glacial till deposited by Pleistocene ice sheets adds calcium-rich material to the region's soils and shallow aquifers, further contributing to water hardness.

The USGS classifies London's 10–13 gpg as Very Hard.

How London Compares to Other Major Cities

CityHardness (gpg)Classification
London, ON (this city) 10–13 gpg Very Hard
Las Vegas, NV 16–17 gpg Very Hard
Phoenix, AZ 16–18 gpg Very Hard
Indianapolis, IN 14–16 gpg Very Hard
Chicago, IL 8–11 gpg Hard
Atlanta, GA 7–9 gpg Moderately Hard
Denver, CO 4–6 gpg Moderately Hard
Seattle, WA 1–3 gpg Soft
Vancouver, BC 0.3–0.6 gpg Soft
US National Average~10 gpgHard

What Hard Water Does to a London Home

At 10–13 gpg, scale damage in London is aggressive. Here's what that looks like in practice:

White calcium carbonate mineral scale buildup on an outdoor faucet — visible within months in hard water cities
White mineral scale on outdoor fixtures becomes visible within months in very hard water areas like London.
💡 Check Your Exact Hardness: Hardness can vary by neighbourhood and distribution zone. City of London Environmental and Engineering Services publishes annual Consumer Confidence Reports with exact hardness data. Well water users should test annually — groundwater hardness varies significantly from municipal supply.

Best Water Treatment for London Homes

At 10–13 gpg, a whole-home water softener is strongly recommended to protect appliances and plumbing. The EPA's Consumer Confidence Report program requires City of London Environmental and Engineering Services to publish annual contaminant data — check it for your specific address.

Fleck 5600SXT 48,000 Grain — Best Overall for London

Industry-standard Fleck valve · Demand-initiated regeneration (saves 30–40% salt) · Most widely serviced softener in the US · Right-sized for Very Hard water

~$450–600

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SpringWell SS4 Smart Water Softener

NSF/ANSI 44 certified · Clack valve · Bluetooth app monitoring · Lifetime tank warranty · Designed for 15–20+ gpg very hard water

~$850–1,050

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APEC ROES-50 Reverse Osmosis System — Drinking Water

NSF certified · Removes 99%+ TDS, chlorine, lead, PFAS, fluoride · Under-sink install · Best paired with a whole-home softener

~$180–220

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Water Hardness Test Kit — Confirm Your GPG Before Buying

Simple test strips · Results in 60 seconds · Well worth $12 before committing to a $500+ softener

~$10–15

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Water softener resin tank and brine salt tank — standard treatment setup for hard water in London
A resin + brine tank setup is the standard whole-home solution for very hard water like London's 10–13 gpg.

See our full best water softeners guide and RO vs water softener comparison for detailed side-by-side recommendations.

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💧 Free: The Hard Water Home Guide

Softener sizing, descaling schedules, and what to test — tailored to very hard water like London's 10–13 gpg.

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London Metro Area — Water Hardness Nearby

Kitchener On14–16 gpg · Very Hard
Toronto On10–12 gpg · Very Hard
Hamilton On12–14 gpg · Very Hard
Windsor On10–13 gpg · Very Hard
Detroit Mi10–13 gpg · Very Hard

Frequently Asked Questions — London Water Hardness

Is London water hard or soft?
London water is Very Hard, averaging 10–13 gpg (171–222 ppm). This is above the US national average of ~10 gpg. London draws from Lake Huron (via Thames River system) + local groundwater.
What is the water hardness in London, ON?
London water hardness is approximately 10–13 gpg (171–222 ppm), classified as Very Hard. City of London Environmental and Engineering Services publishes annual water quality data in its Consumer Confidence Report at www.london.ca.
Why is London water so hard?
London water is hard because of its source geology: Lake Huron (via Thames River system) + local groundwater. The rock formations this water travels through dissolve calcium and magnesium carbonates, producing hard water.
Do I need a water softener in London?
Yes — strongly. At 10–13 gpg, a water softener will measurably extend the life of water heaters, dishwashers, and plumbing. A salt-based ion-exchange softener is the standard recommendation.
Does Kitchener On have similar water hardness to London?
Kitchener On has water hardness of approximately 14–16 gpg — classified as Very Hard. Both cities draw from similar sources and have comparable hardness. See the Kitchener On water hardness guide for details.
How does London water hardness compare to Toronto On?
London averages 10–13 gpg (Very Hard), while Toronto On is approximately 10–12 gpg (Very Hard). They are similar. See the Toronto On water hardness guide.

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