Harlow Water Hardness & Quality Report (2026)

Harlow, the Essex new town established in 1947 on the River Stort in the Lee Valley, is supplied by Affinity Water. Supply is drawn from the River Lee catchment stored in Affinity Water's Lee Valley supply infrastructure, and from licensed boreholes into the Chalk Aquifer beneath east Hertfordshire and west Essex. The River Stort — a tributary of the Lee flowing through Harlow — drains chalk country in the Hertfordshire–Essex border area, carrying chalk-mineral-laden water from the chalk uplands north of Bishop's Stortford. Affinity Water blends Lee Valley surface water with chalk borehole groundwater for distribution to Harlow and the east Hertfordshire area. The new town's rapid post-war population growth required substantial water infrastructure investment in this chalk-rich corner of the Lee watershed.

Harlow's hardness of 225.5 mg/L (15.8°Clark) reflects the Chalk Aquifer contribution from the east Hertfordshire–Essex chalk country. The chalk beneath east Hertfordshire and west Essex is part of the East Anglian Chalk Basin — a thick Cretaceous Upper Chalk sequence that extends continuously from the Chilterns through Hertfordshire into Essex. The Stort valley chalk boreholes and the Lee catchment surface water both carry high dissolved calcium from the chalk outcrop and dip slope. The result is classified as hard by the Drinking Water Inspectorate (DWI) — consistent with the Hertfordshire chalk belt hardness zone.

Limescale is a persistent household challenge in Harlow. At 225.5 mg/L, limescale forms in kettles within two to three weeks and monthly to fortnightly descaling is advisable. Combi-boiler heat exchangers accumulate deposits steadily — annual boiler servicing with a limescale check is important, and fitting an in-line scale inhibitor is recommended. Showerheads, taps, and shower screens develop regular limescale deposits. Washing-up liquid lathers moderately. Using Calgon monthly in the washing machine and maintaining a regular descaling routine is appropriate household limescale management for Harlow's hard chalk supply.