Haverfordwest Water Hardness & Quality Report (2026)

Dŵr Cymru Welsh Water supplies Haverfordwest, the historic county town and former castle borough of Pembrokeshire on the Western Cleddau, from Llys-y-frân Reservoir — the principal water supply reservoir for Pembrokeshire, impounded on the Afon Syfynwy in the southern foothills of the Preseli Hills — treated at Llys-y-frân Water Treatment Works before distribution across south-west Pembrokeshire. At 36 mg/L (2.5°Clark) and a TDS of just 63.6 mg/L, Haverfordwest's water is extremely soft — among the most mineral-free tap water supplies anywhere in Wales or England — reflecting the ancient volcanic and metamorphic rock geology of the Preseli Hills.

Llys-y-frân Reservoir is fed by the Afon Syfynwy and its tributaries draining the southern flanks of the Preseli Hills (Mynydd Preseli) — the ancient landscape of Ordovician igneous rock (dolerite, rhyolite, and tuff) and Silurian shale, most famous as the source of the Stonehenge bluestones. These Ordovician igneous rocks are highly resistant to weathering and yield virtually no dissolved calcium or mineral load to the runoff. The resulting 36 mg/L hardness and TDS just 63.6 mg/L is the characteristic extremely soft water produced by the ancient hard-rock landscape of west Wales.

At 36 mg/L, limescale is virtually non-existent as a household concern in Haverfordwest. Kettles may need only a very occasional light wipe every four to six months at most. The combi-boiler requires no meaningful scale protection, though a basic inhibitor is always sensible practice. Washing-up liquid lathers abundantly with the smallest quantities. Taps and shower heads remain pristine with essentially no mineral deposits. In any older property with lead or copper pipework, Haverfordwest's extremely soft, naturally slightly corrosive water warrants briefly running the cold tap before drinking — Welsh Water's standard precautionary advice throughout the Pembrokeshire soft water supply zone.