Hertfordshire hard water map: limescale severity by postcode, and what actually works

Every Hertfordshire home we clean has limescale. The question is how much, and what to do about it. I pulled the Affinity Water quality reports for every supply zone in the county, cross-referenced them against the postcodes our cleaners cover, and ran a 12-product test in 40 homes over four months. The results changed which products our vans carry.

The hardness map

Water hardness is measured in milligrams per litre of calcium carbonate (CaCO3). The threshold for 'hard' is 200 mg/L. 'Very hard' starts at 300. Every supply zone Affinity Water runs in Hertfordshire reads above 240, and three zones around the chalk aquifer near Hitchin read above 320.

• SG4, SG5 (Hitchin, Letchworth): 320 to 340 mg/L. The hardest in the county.
• AL1, AL3, AL4 (St Albans, Harpenden): 290 to 310 mg/L.
• SG1, SG2 (Stevenage): 280 to 300 mg/L.
• WD17, WD18, WD25 (Watford): 250 to 280 mg/L.
• HP1 to HP4 (Hemel Hempstead, Berkhamsted): 240 to 270 mg/L.
• EN6 to EN10 (Potters Bar, Cheshunt): 260 to 290 mg/L.

Where it shows first

1. 1Kettle element — within a week of moving in.
2. 2Shower glass — 3 to 4 weeks before the film becomes visible.
3. 3Tap aerators — clog noticeably at 6 to 8 weeks.
4. 4Toilet bowl waterline — visible ring at 8 to 12 weeks.
5. 5Dishwasher heating element — efficiency drops 15 percent in 18 months without descaling.

The 12-product test

We tested every limescale remover stocked by Waitrose, Sainsbury's, B&Q and a trade catalogue across 40 homes. Same surface (chrome shower head with 6 weeks of buildup), same dwell time (5 minutes), same wipe. Scored on residue, scent, and damage to the underlying chrome under a 10x loupe.

The 3 that worked

• Viakal Original. Dissolved 95 percent of scale in 5 minutes. Heavy scent. Avoid on enamel and natural stone.
• HG Professional Lime Scale Remover. 92 percent. Lower scent. Costs 40 percent more per litre but lasts 60 percent longer at recommended dilution.
• Citric acid powder at 50g per 500ml warm water. 88 percent. Cheapest by far, food-safe, scent-free. The product our team uses on natural stone and brass.

The 9 that did not

Six supermarket own-brand sprays scored under 60 percent and left a sticky surfactant film that re-attracted scale within a week. Two eco brands (which I will not name without testing again in 2026) scored well on chrome but stripped the lacquer off brushed brass. One traditional 'thick' descaler ran straight off the vertical chrome surface before it had time to work.

What to do, by home type

New-build flat with chrome fittings

Wipe shower glass with a microfibre after every shower. One Viakal pass per fortnight on the screen and the tap. Descale the kettle monthly with a tablespoon of citric acid in boiling water.

Victorian terrace with original brass

Avoid acid sprays on the brass. Citric acid solution at low concentration, applied with a soft cloth, rinsed with clean water, dried immediately. Twice a month is plenty.

Family home with a dishwasher and a washing machine

Run a dishwasher tablet through both machines monthly. Consider a salt-block water softener: in the SG postcodes the payback is real, and the long-term saving on the washing machine drum is substantial.

What to watch in 2026

Affinity Water is trialling a calcite contactor at its Egham works that would reduce hardness in the southern supply zone by around 60 mg/L from 2027. WD and parts of HP would see the largest drop. The northern chalk aquifer feeding SG postcodes is not part of the trial, so Hitchin will stay at the top of the hardness map for the foreseeable future.