Tap water in GU5 (Guildford District West): coffee, brewing suitability
Supplied by Thames Water
Tap water in Guildford District West, supplied by Thames Water, has the character of a chalk aquifer source, typical of southern and eastern England. It’s slightly hard, around the national midpoint, with a total hardness of 197 mg/L as CaCO₃.
Mineral composition
| mg/L | |
|---|---|
| Calcium | 74 |
| Magnesium | 3 |
| Sodium | 20 |
| Sulfate | 36 |
| Chloride | 36 |
| Bicarbonate | 167 |
Additional info
| Hardness | 197 as CaCO₃ |
| Alkalinity | 137 as CaCO₃ |
| pH | 7.3 |
| Conductivity | 492 µS/cm |
| Source | Thames Water |
| Data year | 2024 |
What this means
Kettle & appliances
Light limescale will accumulate in kettles and on heating elements over weeks. A periodic descale (monthly or so) will keep things in check, but it’s not urgent.
Espresso
Hardness at this level starts to affect espresso machines more noticeably. Scale will form in boilers over months, and the water’s buffering will round off some of the brighter acidity in the cup. Regular descaling becomes worthwhile.
Filter & pour-over
Filter coffee starts to lose some of its top-end brightness here. Lighter roasts will taste rounder and less distinctive than they would with softer water, though medium and darker roasts hold up well. The cup won’t be flat, but the crispest acidity is softened.
Drinking & cooking
A faint mineral taste may be noticeable if you’re paying attention. Vegetables and pulses cook normally; rice and pasta are unaffected.
Bicarbonate
Significant buffering that pushes mash pH high enough to require acid additions for most beer styles other than stouts, and produces espresso that is notably flat and heavy, with muted acidity and a tendency toward a uniform, opaque flavour profile.
Get the best from your water
GU5 tap water works well for espresso, brewing, baking, and aquarium use with little or no adjustment. It has too much mineral content for tea and horticulture; a bottled water blend is the better route for those.
Nearby areas
Data sourced from Thames Water (2024). Looking for a specific address? Look up your full postcode for the most accurate result.