Didcot Water Hardness & Quality Report (2026)

Thames Water provides Didcot's water supply, drawing from the River Thames and groundwater aquifers within the Chiltern Hills. Key abstraction points include sites along the River Thames like Wraysbury and Datchet, with groundwater sourced from boreholes in the Chilterns, such as those feeding Mongewell and Harwell treatment works. Water is treated at facilities like Drayton and Sutton Courtney before reaching residents. The supply is a blend of surface and groundwater, ensuring reliability for the millions served across London and the Thames Valley.

The geology underpinning Didcot's water is characterized by permeable Cretaceous Chalk and Jurassic limestones. These formations create productive aquifers that naturally pick up dissolved minerals from percolating rainwater. The dissolution of calcium-bearing rocks, particularly in the Chalk Group and Lower Greensand, significantly elevates the water's natural mineral content. This process results in a characteristically hard water supply, with the Eocene Reading Beds clays also playing a role in the mixed surface-groundwater chemistry found throughout Oxfordshire.

Homeowners in Didcot will likely notice limescale buildup in appliances like kettles, boilers, and washing machines, which can reduce their efficiency and lifespan. Hot water systems and heating elements are particularly susceptible to chalky deposits. Regular descaling with common household agents like vinegar or citric acid can help manage this. Some residents opt for whole-house water softeners to combat the long-term effects of hard water, though this can introduce sodium into the supply. The water's pH typically ranges between 7.2 and 7.8, and Thames Water monitors for various contaminants, including lead, pesticides, and nitrates, ensuring the water meets stringent UK standards.