Merthyr Tydfil Water Hardness & Quality Report (2026)
Water Hardness
6.3°Clark9.1°fH5.1°dH
Source
reservoir
pH Level
7.5
neutral = 7.0
Lead
0.003 mg/L
✓ Below action level
TDS
175.5 mg/L
Est. Daily Cost
£0.21
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 Merthyr Tydfil, your appliances are currently losing 12% efficiency due to mineral buildup.
| Appliance | In Merthyr Tydfil | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 6.6 yrs | 8.5 yrs | -22% |
| Washing Machine | 10.3 yrs | 12 yrs | -14% |
| Water Heater | 12 yrs | 15 yrs | -20% |
Regional Water Comparison
How Merthyr Tydfil compares to its nearest neighbours
| City | Hardness | Clark° | Risk | Source |
|---|---|---|---|---|
| ▶ Merthyr Tydfil, Wales | 90.5 mg/L | 6.3° | 🟡 Moderately Hard | reservoir |
| Mountain Ash, Wales | 71 mg/L | 5° | 🟡 Moderately Hard | reservoir |
| Aberdare, Wales | 79 mg/L | 5.5° | 🟡 Moderately Hard | reservoir |
| Treharris, Wales | 109 mg/L | 7.6° | 🟡 Moderately Hard | reservoir |
| Rhondda, Wales | 68 mg/L | 4.8° | 🟡 Moderately Hard | reservoir |
National Benchmark
How Merthyr Tydfil compares to the United Kingdom average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Merthyr Tydfil | 90.5 mg/L | 🟡 Low |
| United Kingdom National Avg | 183 mg/L | 🔴 High |
| Livingston Top Rated | 8.5 mg/L | 🟢 None |
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What Makes Merthyr Tydfil's Water Unique?
Local geology and source profile
Merthyr Tydfil, the south Wales valleys town at the head of the Taff valley in Merthyr Tydfil County Borough, is supplied by Dŵr Cymru Welsh Water from the Taf Fechan Reservoirs — Pontsticill Reservoir and Pentwyn Reservoir — impounding the headwaters of the Taf Fechan on the Brecon Beacons plateau north of Merthyr. The Taf Fechan rises on the Carboniferous Sandstone (Millstone Grit) and Devonian Old Red Sandstone moorland of the Brecon Beacons, draining the Beacons plateau above the limestone escarpment. The Beacons plateau moorland is of largely insoluble sandstone and gritstone, producing soft upland reservoir water. Welsh Water treats at the Pontsticill Treatment Works and distributes to Merthyr Tydfil and the upper Taff valley.
Merthyr Tydfil's soft water — 90.5 mg/L (6.3°Clark) — reflects the Carboniferous Sandstone and Devonian Old Red Sandstone moorland catchment of the Taf Fechan, slightly harder than coastal south Wales valleys supply zones due to the moderate influence of the Carboniferous Limestone of the Brecon Beacons escarpment fringe on the Taf Fechan catchment margins. The Drinking Water Inspectorate Wales classifies this supply as soft.
Limescale is minor in Merthyr Tydfil. At 90.5 mg/L, limescale builds slowly and kettles need descaling every two to three months. Combi-boiler heat exchangers accumulate minimal deposits; annual servicing is routine. Showerheads and taps remain largely clear. Washing-up liquid lathers very well with the soft Brecon Beacons supply. Limescale is not a significant domestic concern for Merthyr Tydfil households on the Taf Fechan reservoir supply.
Geology & Source: Supplied by Dŵr Cymru Welsh Water from the Taf Fechan Reservoirs — Pontsticill and Pentwyn — in the Brecon Beacons — Merthyr Tydfil's position at the head of the Taff valley draws on Welsh Water's upland reservoir supply from the Carboniferous Old Red Sandstone and Beacons plateau, producing soft water at 90.5 mg/L (6.3°Clark).