London tap water ranks among Britain's worst for brewing coffee, study finds

London may be Britain's coffee capital, but its tap water is not ideally suited to brewing a great cup at home. According to a new analysis by speciality coffee retailer Rave Coffee, every London postal district sits below the national average for water quality when assessed against measures set out by the Specialty Coffee Association (SCA).

Rave Coffee created their ‘Coffee Water Index’, scoring all 120 UK postcode areas in England, Wales and Scotland, covering 66,706 individual postcodes, against five water quality measures known to affect how coffee tastes.

These measures include water alkalinity and hardness, the amount of chlorine present, as well as conductivity and pH. The closer a postcode area's tap water sits within those targets, the higher it scored out of 100.

How does London's tap water rank for brewing coffee?

Despite the capital's reputation for its coffee culture, London's tap water is comparatively poor for brewing it. All eight London postcode areas included in the study scored below the national average of 57.6 in the Coffee Water Index, with scores ranging from 39.2 to 47.3 out of 100. This placed every London area within the bottom third of the 120 postcode areas studied, highlighting a potential contrast between the capital’s thriving coffee culture and the quality of its brewing water.

North London performed best among the eight areas, ranking 87th overall with a score of 47.3. At the other end of the table, East London ranked 112th, scoring just 39.2, making it the lowest-performing London postcode area in the study. Other areas also struggled, including South East London (45.7), West London (45.5) and South West London (41.0). The findings suggest that, despite the abundance of specialist coffee shops and skilled baristas across the capital, the quality of local tap water could be a factor affecting the coffee brewing process.

The postcodes with the best tap water for brewing coffee

Lerwick takes the top spot scoring 84.7 out of 100. The postcode area, which is supplied by Scottish Water, was found to offer tap water that was closest to the ideal composition for making coffee.

Its water has a hardness reading of 55.8mg/L of calcium carbonate (CaCO3), which is just short of the SCA's 68mg/L ideal for preparing coffee, and its low levels of chlorine (0.07mg/L), were close to the ideal target of zero.

Kirkwall takes second place (81.1 out of 100), owing to a low chlorine reading of 0.15mg/L and  near optimal water hardness at 88.4mg/L CaCO3. It also performed well for conductivity, reading 286.7μS/cm against the 230μS/cm target.

Aberdeen ranks third (81.1 out of 100) performing well across the board, with water hardness at 44.3mg/L, among the lowest chlorine levels, at 0.12mg/L and a conductivity measure of 169.1μS/cm.

The postcode with the least suitable tap water for brewing coffee

The Ipswich postcode code area, which is supplied by Anglian Water and Essex & Suffolk Water, was found to offer the least suited tap water for making coffee, scoring just 28.9 out of 100.

The area had the second hardest water reading in the entire study behind Colchester, at 371.9mg/L CaCO3. It also has the highest alkalinity reading, at 326.4mg/L CaCO3 against a 40mg/L ideal.

Ashlee Eastwood-Quinn, Head of Coffee at Rave Coffee, commented:

“When preparing coffee at home, what comes out of your tap matters just as much as the type of coffee you’re using. A lot of the time people dial in grind size and brew ratios, but water is the one variable most people overlook, even though it makes up around 98% of the cup.”

“If you live in one of the postcode areas that performs less well, it doesn't mean good coffee is out of reach. Opting to use filtered water can make a huge difference to the quality of your coffee experience.”