Cardiff Water Hardness & Quality Report (2026)
Water Hardness
2.8°Clark4°fH2.2°dH
Source
reservoir
pH Level
7.3
neutral = 7.0
Lead
0.002 mg/L
✓ Below action level
TDS
75 mg/L
Est. Daily Cost
£0.09
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 Cardiff, your appliances are currently losing 5% efficiency due to mineral buildup.
| Appliance | In Cardiff | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 8.3 yrs | 8.5 yrs | -2% |
| Washing Machine | 12.1 yrs | 12 yrs | — |
| Water Heater | 14 yrs | 15 yrs | -7% |
Regional Water Comparison
How Cardiff compares to its nearest neighbours
| City | Hardness | Clark° | Risk | Source |
|---|---|---|---|---|
| ▶ Cardiff, Wales | 40 mg/L | 2.8° | 🟢 Soft | reservoir |
| Bristol, South West | 228.5 mg/L | 16° | 🔴 Very Hard | reservoir |
| Swansea, Wales | 35 mg/L | 2.5° | 🟢 Soft | reservoir |
| Swindon, South West | 273.5 mg/L | 19.2° | 🔴 Very Hard | mixed |
| Plymouth, South West | 45 mg/L | 3.2° | 🟢 Soft | reservoir |
National Benchmark
How Cardiff compares to the United Kingdom average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Cardiff | 40 mg/L | 🟢 None |
| United Kingdom National Avg | 164 mg/L | 🟠 Moderate |
| Glasgow Top Rated | 15 mg/L | 🟢 None |
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What Makes Cardiff's Water Unique?
Local geology and source profile
Cardiff's water supply is managed by Dŵr Cymru Welsh Water, Wales' not-for-profit water and sewerage company, with principal sources in the upland reservoirs of the Brecon Beacons and the Taff Fawr valley. The Llwyn-on Reservoir (completed 1926), Cantref Reservoir, and Beacons Reservoir form a cascade system in the upper Taff valley, delivering gravity-fed water to Cardiff and the South Wales valleys. Water is treated at Llanishen Water Treatment Works to the north of the city before distribution to Cardiff's urban and suburban network. Welsh Water is distinctive among UK water companies in having operated as a not-for-profit organisation since 2001, with any surplus reinvested in the network rather than paid as dividends.
Cardiff's softness of 40 mg/L (2.8°Clark) derives from the geology of the Brecon Beacons catchment. The upper Taff valley reservoirs are fed by rainfall draining over Devonian Old Red Sandstone — a coarse, iron-rich continental sedimentary rock that dissolves poorly in water and contributes negligible calcium. The surrounding high ground includes Silurian and Ordovician mudstones and shales that are similarly resistant to weathering. The resulting water is classified as very soft by the Drinking Water Inspectorate — typical of Welsh Water's predominantly upland reservoir supply across South Wales.
Limescale problems are rare in Cardiff homes. At 40 mg/L, limescale accumulates very slowly — most Cardiff residents need to descale their kettle only once or twice a year, and limescale on taps and showerheads is minimal. The combi-boiler in a Cardiff property is under very little stress from limescale, and heat exchanger deposits are unlikely to accumulate to efficiency-reducing levels for many years without water treatment. Washing-up liquid lathers freely and generously. As with other soft-water Welsh cities, the main consideration is occasional inspection of older copper and lead pipework for corrosion — Welsh Water maintains pH treatment at the works to mitigate this risk.
Geology & Source: Supplied by Dŵr Cymru Welsh Water from Llwyn-on Reservoir and upland catchments in the Brecon Beacons — water draining over Devonian Old Red Sandstone and Silurian mudstone in these Welsh uplands dissolves minimal calcium, producing very soft water at 40 mg/L (2.8°Clark).