SG4 tap water: what's in it?
Affinity Water: at least 20 tests failed UK drinking-water standards in 2025 (DWI, company-wide).
Some published DWI figures don't reconcile or identify a company, so we've left them out; the true number may be higher. England overall: 99.97% of tests met standards.
SG4 tap water quality report · 2026
Hardness
Very hard
Hitchin (supply zone) · 1 January 2025 to 31 December 2025
Details
Hitchin (supply zone) · 1 January 2025 to 31 December 2025
Hosepipe ban
In force in part of Affinity Water's area
A ban has been reported, but the notice doesn't confirm which parts of the supply area it covers. Check with your water company before using a hosepipe. Checked 11 October 2026 at 02:34
Details
A ban has been reported, but the notice doesn't confirm which parts of the supply area it covers. Check with your water company before using a hosepipe. Checked 11 October 2026 at 02:34
Storm overflows
13 overflows within 10 km of SG4 centre
137 spills in 2025
Details
137 spills in 2025
Lead pipes
59% built before 1973
Estimate, not a test. Homes in the parts of SG4 we can match to council-tax records (100% of its postcodes) whose build period is known; the share with no recorded build period isn't published for these areas. Allowing for suppressed counts: 57–59%. England and Wales: 61% (2026).
Details
Estimate, not a test. Homes in the parts of SG4 we can match to council-tax records (100% of its postcodes) whose build period is known; the share with no recorded build period isn't published for these areas. Allowing for suppressed counts: 57–59%. England and Wales: 61% (2026).
Who supplies water in SG4
Supplies 906 of 906 postcodes (100%)
Affinity Water's phone number isn't in our records; their contact page lists it.
We can't tell your sewerage company from official data for this area. It's named on your water bill.
Drinking-water test record
Affinity Water: 906 of 906 postcodes
Affinity Water
Affinity Water, company-wide
- Regulator
- DWI
- Report year
- 2025
- Failed tests
- Not shown
- Tests
- 189,963
The regulator's published total and its company rows disagree, so we don't show a count.
| Parameter | Failed tests |
|---|---|
| E. coli (confirmed) | Failed tests: 4 |
| Enterococci (confirmed) | Failed tests: 2 |
| Iron | Failed tests: 1 |
| Lead | Failed tests: 6 |
| Nickel | Failed tests: 3 |
| Total coliforms (confirmed) | Failed tests: 4 |
Source: DWI england 2025, Annex B — dated 6 July 2026, read 13 October 2026
Source: DWI england 2025, Annex A — dated 6 July 2026, read 13 October 2026
England: 99.97% of tests met standards in 2025 (DWI).
Source: DWI england 2025, national compliance — dated 6 July 2026, read 13 October 2026
How hard is the water in SG4?
55% of SG4's postcodes are in the Hitchin supply zone (Affinity Water): 368 mg/l, very hard.
Hitchin · Affinity Water (501 of 906 postcodes)
368 mg/l · 25.8 °Clark · 20.6 °dH · 36.8 °fH
Zone average.
Hitchin (supply zone) · 1 January 2025 to 31 December 2025
Source: Affinity Water — dated 1 January 2025 to 31 December 2025, read 29 September 2026
7 identified supply zones in SG4
Hitchin · Affinity Water (501 of 906 postcodes)
368 mg/l · 25.8 °Clark · 20.6 °dH · 36.8 °fH
Zone average.
Hitchin (supply zone) · 1 January 2025 to 31 December 2025
Source: Affinity Water — dated 1 January 2025 to 31 December 2025, read 29 September 2026
Offley/Kimpton · Affinity Water (217 of 906 postcodes)
337 mg/l · 23.6 °Clark · 18.9 °dH · 33.7 °fH
From the company's postcode lookup.
Offley/Kimpton (supply zone) · read on 29 September 2026
Source: Affinity Water — read 29 September 2026
Baldock/Letchworth · Affinity Water (78 of 906 postcodes)
318 mg/l · 22.3 °Clark · 17.8 °dH · 31.8 °fH
Zone average.
Baldock/Letchworth (supply zone) · 1 January 2025 to 31 December 2025
Source: Affinity Water — dated 1 January 2025 to 31 December 2025, read 29 September 2026
Knebworth/Tewin · Affinity Water (11 of 906 postcodes)
296 mg/l · 20.8 °Clark · 16.6 °dH · 29.6 °fH
From the company's postcode lookup.
Knebworth/Tewin (supply zone) · read on 29 September 2026
Source: Affinity Water — read 29 September 2026
Stevenage · Affinity Water (6 of 906 postcodes)
321 mg/l · 22.5 °Clark · 18.0 °dH · 32.1 °fH
From the company's postcode lookup.
Stevenage (supply zone) · read on 29 September 2026
Source: Affinity Water — read 29 September 2026
Welwyn Garden City · Affinity Water (1 of 906 postcodes)
319 mg/l · 22.4 °Clark · 17.9 °dH · 31.9 °fH
From the company's postcode lookup.
Welwyn Garden City (supply zone) · read on 29 September 2026
Source: Affinity Water — read 29 September 2026
Harpenden · Affinity Water (1 of 906 postcodes)
332 mg/l · 23.3 °Clark · 18.6 °dH · 33.2 °fH
From the company's postcode lookup.
Harpenden (supply zone) · read on 29 September 2026
Source: Affinity Water — read 29 September 2026
91 postcodes without an identified supply zone
Affinity Water (91 of 906 postcodes)
We do not have a verified hardness figure for this area. Ask your water company for its water quality report.
Storm overflows nearby
13 overflows within 10 km of SG4 centre · 137 spills in 2025
SG4 (district) · 2025
Source: Environment Agency EDM annual return 2025 — dated 20 August 2026, read 13 October 2026
Overflows here are run by Anglian Water and Thames Water.
9 of these were monitored for only part of 2025.
Nearest 5 shown
POUND FARM PUMPING STATION
Into Purwell · 1.6 km from the centre of SG4
2 spills · 2.5 hours · Monitored 100% of 2025
ASHBROOK WATER RECYCLING CENTRE
Into ASH BROOK, RIVER GREAT OUSE NT · 1.7 km from the centre of SG4
7 spills · 79.2 hours · Monitored 100% of 2025
BANCROFT RECREATION GROUND CSO
Into River Hiz · 3.7 km from the centre of SG4
0 spills · 0 hours · Monitored 100% of 2025
WHITWELL WWTW
Into RIVER MIMRAM · 5.3 km from the centre of SG4
13 spills · 96 hours · Monitored 95.5% of 2025
HITCHIN WATER RECYCLING CENTRE
Into River Hiz · 5.4 km from the centre of SG4
3 spills · 0.5 hours · Monitored 99.9% of 2025
Annual 2025 figures from monitored overflows. Not live, and not a bathing-water or tap-water verdict.
- 57 England outfalls in the 2025 return had no usable location and aren't counted.
- Northern Ireland isn't covered: No licensed annual per-outfall source in the approved source list; BT postcode coordinates require an LPS licence.
Older homes and lead pipes
59% built before 1973
59% of homes here were built before 1973 — estimate, not a test.
Homes in the parts of SG4 we can match to council-tax records (100% of its postcodes) whose build period is known; the share with no recorded build period isn't published for these areas. Allowing for suppressed counts: 57–59%. England and Wales: 61% (2026).
Older homes are more likely to have lead pipes. Only a test tells you whether yours does.
SG4 (district) · 2026
Source: Valuation Office Agency, Council Tax: stock of properties — dated 31 March 2026, read 24 September 2026
Fluoride
We cannot confirm whether this area is part of a water fluoridation scheme. Ask your water supplier using your postcode.
Around one in ten people in England receive drinking water supplied by a fluoridation scheme.
England · 2026 health monitoring report
Source: UKHSA and DHSC — dated 30 March 2026, read 13 October 2026
Hosepipe bans
What you can do
As an Amazon Associate we earn from qualifying purchases. Links go to amazon.com; Amazon's Earn Globally service can localise them to amazon.co.uk. Check the model and UK delivery before buying.
Water filter jugs
LifeStraw
LSH7GLSPK21
Performance certification:
Certified by WQA to NSF/ANSI 42 for Aesthetic Chlorine and Taste and Odor; Certified by WQA to NSF/ANSI 53 for Lead and Mercury; Certified by WQA to NSF/ANSI 401 for Microplastics (a US/international standard; it is not UK approval)
View Detailsreduces chlorine taste and odour in drinking water.
A UK retailer lists this model. Amazon UK stock and delivery are unverified; this Amazon link may not ship to the UK. Check the exact model and UK delivery before you pay.
UK availability evidence checked 14 October 2026.
Shower filters
Weddell Water
WD-100BL
Performance certification:
Certified by NSF to NSF/ANSI 177 for Free Available Chlorine Reduction (a US/international standard; it is not UK approval)
View Detailsreduces chlorine in shower water; does not soften water.
A UK retailer lists this model. Amazon UK stock and delivery are unverified; this Amazon link may not ship to the UK. Check the exact model and UK delivery before you pay.
Check it fits your shower fitting before buying; a US fitting may need an adaptor.
UK availability evidence checked 14 October 2026.
We haven't verified a water softener for UK buyers yet.
What a pick has to pass:
- An exact-model listing from NSF, WQA or IAPMO for the model sold in the UK
- Listed to NSF/ANSI 44, the water softener standard
- The manufacturer's documented feed connection and water-pressure range, so a plumber can check them against UK pipework
- UK availability evidenced by Amazon UK, the manufacturer or a UK retailer, checked in the last 90 days
Until we can recommend one, see what a softener costs to buy, fit and run in the UK. Water softener cost
We haven't verified a lead test kit for UK buyers yet.
What a pick has to pass:
- A lead result reported by a laboratory accredited for that test (UKAS, ISO/IEC 17025), named on the kit's listing
- UK availability evidenced by Amazon UK, the manufacturer or a UK retailer, checked in the last 90 days
Start with your water company: if you think you have lead pipes, you can ask it to test the water at your kitchen tap. Which water test you need
Common water problems
How much does a water softener cost in the UK?
Water softener cost UK 2026: price by home size
Why is my tap water cloudy or white?
Why is my tap water cloudy or white? (UK)
Brown tap water: causes and what to do (UK)
Why does my tap water taste metallic?
Tap water tastes metallic? Causes and fixes (UK)
Questions about tap water in SG4
- Is the water in SG4 hard or soft?
- Affinity Water: very hard, 368 mg/l, 25.8 °Clark, 20.6 °dH, 36.8 °fH (Hitchin (supply zone), 1 January 2025 to 31 December 2025). Zone average. Affinity Water: very hard, 337 mg/l, 23.6 °Clark, 18.9 °dH, 33.7 °fH (Offley/Kimpton (supply zone), read on 29 September 2026). From the company's postcode lookup. Affinity Water: We do not have a verified hardness figure for this area. Ask your water company for its water quality report. Affinity Water: very hard, 318 mg/l, 22.3 °Clark, 17.8 °dH, 31.8 °fH (Baldock/Letchworth (supply zone), 1 January 2025 to 31 December 2025). Zone average. Affinity Water: hard, 296 mg/l, 20.8 °Clark, 16.6 °dH, 29.6 °fH (Knebworth/Tewin (supply zone), read on 29 September 2026). From the company's postcode lookup. Affinity Water: very hard, 321 mg/l, 22.5 °Clark, 18.0 °dH, 32.1 °fH (Stevenage (supply zone), read on 29 September 2026). From the company's postcode lookup. Affinity Water: very hard, 319 mg/l, 22.4 °Clark, 17.9 °dH, 31.9 °fH (Welwyn Garden City (supply zone), read on 29 September 2026). From the company's postcode lookup. Affinity Water: very hard, 332 mg/l, 23.3 °Clark, 18.6 °dH, 33.2 °fH (Harpenden (supply zone), read on 29 September 2026). From the company's postcode lookup.
- What does the drinking water regulator's record show for SG4?
- Affinity Water: at least 20 tests failed UK drinking-water standards in 2025 (DWI, company-wide). Some published DWI figures don't reconcile or identify a company, so we've left them out; the true number may be higher. England overall: 99.97% of tests met standards.
- Could homes in SG4 have lead pipes?
- 59% of homes here were built before 1973 — estimate, not a test. Homes in the parts of SG4 we can match to council-tax records (100% of its postcodes) whose build period is known; the share with no recorded build period isn't published for these areas. Allowing for suppressed counts: 57–59%. England and Wales: 61% (2026). Older homes are more likely to have lead pipes. Only a test tells you whether yours does.
- Is the water in SG4 fluoridated?
- We cannot confirm whether this area is part of a water fluoridation scheme. Ask your water supplier using your postcode. Around one in ten people in England receive drinking water supplied by a fluoridation scheme.
Sources and method
- Water Company Boundaries (UC2) ↗ · 19 September 2026 · read 20 September 2026
- DWI england 2025, Annex B ↗ · 2025 · read 13 October 2026
- DWI england 2025, national compliance ↗ · 2025 · read 13 October 2026
- Affinity Water ↗ · 1 January 2025 to 31 December 2025 · read 29 September 2026
- Affinity Water ↗ · read on 29 September 2026 · read 29 September 2026
- Environment Agency EDM annual return 2025 ↗ · 2025 · read 13 October 2026
- Valuation Office Agency, Council Tax: stock of properties ↗ · 2026 · read 24 September 2026
- UKHSA and DHSC ↗ · 2026 health monitoring report · read 13 October 2026
- Environment Agency ↗ · 11 October 2026 · read 11 October 2026
Affinity Water, Affinity Water, Affinity Water, Affinity Water, Affinity Water, Affinity Water, Affinity Water: Database right, used under the publisher's terms.
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