Windsor Water Hardness & Quality Report (2026)
Water Hardness
22.1°Clark31.5°fH17.6°dH
Source
mixed
pH Level
8.5
neutral = 7.0
Lead
0.006 mg/L
✓ Below action level
TDS
940.9 mg/L
Est. Daily Cost
£0.71
energy & soap waste
Source: DWI Data Portal · Updated 2026
0–60
mg/L
Soft
61–120
mg/L
Moderately Hard
121–180
mg/L
Hard
180+
mg/L
Very Hard
Appliance Damage Report
In Windsor, your appliances are currently losing 42% efficiency due to mineral buildup.
| Appliance | In Windsor | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 1.5 yrs | 8.5 yrs | -82% |
| Washing Machine | 3 yrs | 12 yrs | -75% |
| Water Heater | 5 yrs | 15 yrs | -67% |
Regional Water Comparison
How Windsor compares to its nearest neighbours
| City | Hardness | Clark° | Risk | Source |
|---|---|---|---|---|
| ▶ Windsor, South East | 314.5 mg/L | 22.1° | 🔴 Very Hard | mixed |
| Slough, South East | 238 mg/L | 16.7° | 🔴 Very Hard | mixed |
| Egham, South East | 223 mg/L | 15.6° | 🔴 Very Hard | mixed |
| Burnham, South East | 299 mg/L | 21° | 🔴 Very Hard | mixed |
| Sunninghill, South East | 178.5 mg/L | 12.5° | 🟠 Hard | mixed |
National Benchmark
How Windsor compares to the United Kingdom average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Windsor | 314.5 mg/L | 🔴 High |
| United Kingdom National Avg | 183 mg/L | 🔴 High |
| Livingston Top Rated | 8.5 mg/L | 🟢 None |
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What Makes Windsor's Water Unique?
Local geology and source profile
Windsor, the historic Royal Borough town on the south bank of the Thames opposite Eton in Berkshire, is served by Thames Water. Despite its riverside setting, Windsor's supply draws heavily on deep groundwater from the Thames Valley and Berkshire Chalk Aquifer, pumped from boreholes sunk into the Cretaceous chalk beneath the Windsor/Maidenhead area. Thames Water supplements this with surface abstraction treated at Hampton and Walton Water Treatment Works, but the extremely high TDS of 940.9 mg/L — among the highest in England — indicates that a very large fraction of Windsor's supply is derived from long-residence deep chalk groundwater rather than diluting river water. The water is distributed through Thames Water's south Berkshire and outer west London trunk network.
The Upper Cretaceous Chalk beneath Windsor is deeply confined and hydraulically connected to the Chiltern Hills chalk recharge zone to the north. Groundwater here has residence times of many decades, during which calcium bicarbonate dissolves to saturation from the chalk matrix. Sulphate and sodium from deeper mineralised aquifer horizons and from the Reading Beds (Paleocene) above the chalk contribute additional dissolved solids, pushing TDS to exceptional levels. The chalk beneath the Thames terrace at Windsor has some of the highest intrinsic hardness of any aquifer in Britain.
At 314.5 mg/L Windsor has extremely hard water, and limescale is relentless. Kettle elements fur over within days and should be descaled at least weekly with citric acid. Shower screens coat rapidly — daily wiping and weekly limescale treatment are routine tasks. Combi-boilers are at serious risk from scale accumulation and should have magnetic scale inhibitors installed on supply lines; regular servicing is essential. Washing-up liquid produces little lather and excessive quantities must be used. A whole-house water softener is strongly recommended for Windsor households and will pay for itself in saved appliance repairs within a few years.
Geology & Source: Supplied by Thames Water from deep boreholes into the Thames Valley Chalk Aquifer and the River Thames abstraction at Surbiton and Hampton — Chiltern and Berkshire chalk groundwater — produces extremely hard water at 314.5 mg/L (22.1°Clark).