Poly and perfluoroalkyl substances (PFAS)

In August 2024, the Inspectorate updated its guidance to the industry regarding requirements to submit test results and summary risk assessment information for PFAS. Companies have continued with their targeted sampling strategy to focus on those sites which are likely to be at risk from PFAS contamination. In 2024, companies in England and Wales collectively carried out over 770,000 analyses for individual PFAS, and in total, over 1.8 million analyses have been performed since 2012, providing a significant dataset to understand the challenges in drinking water.

PFAS tiers are now applied to any PFAS chemicals of interest detected in the final or raw water. Sites are classified as:

Tier 1 where PFAS concentrations are <0.01 µg/L.
Tier 2 where PFAS concentrations are <0.1 µg/L.
Tier 3 where PFAS concentrations are ≥0.1 µg/L

PFAS tiers are to be applied to all PFAS chemicals of interest identified in the parameter list (Annex C of the Information Direction) detected in final water. The latest guidance on the actions companies should be taking for the three tier levels is available in the Inspectorate’s most recent guidance – DWI_PFAS-Guidance_Mar_2025.pdf

Monitoring by water companies has highlighted a further PFAS of potential concern; 6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB). This compound has been added to the parameter list and companies are expected to initiate monitoring and reporting for this parameter as soon as practicable.

Companies are also expected to consider the effect of combined concentrations of the PFAS chemicals of interest identified in the parameter list. As such, the requirement to implement a prioritised mitigation methodology to progressively reduce PFAS concentrations in drinking water has been further extended to include combined PFAS on a ‘sum of’ basis. Companies have now implemented reporting for the ‘sum of PFAS’ based on the 48 named PFAS in the parameter list. Where sites fall into tier 2 or 3 for the sum of parameter these sites should be rolled into the existing site prioritisation approach based on their relative classification and an appropriate risk reduction strategy should aim to progressively reduce PFAS concentrations in drinking water. The Inspectorate’s three tier system is a risk-based system intended to prioritise the supply systems which require additional controls. The analysis targets the source water because this provides information on the hazard and what the necessary mitigation should be, be that blending, removal of the source water or treatment. During 2024, there were no samples reported in tier 3 for any treated water being supplied to consumers. In total 351 tests of raw water abstractions had results within tier 3. This helps to demonstrate that the current industry strategy of mitigating the risks from PFAS is working effectively to protect consumers. Ninety-six percent of the tests were less than the detection limit for their analytical methodology.

Table 10 Total number of tests in England including all results less than limit of detection

Tier	Raw water tests	Treated water tests	Total
Tier 1	287,840	413,084	700,924
Tier 2	28,888	17,223	46,111
Tier 3	351	0	292
Total	317,079	430,307	747,386

Table 11 Total number of tests in Wales, not including results less than limit of detection

Tier	Raw water tests	Treated water tests	Total
Tier 1	75	443	518
Tier 2	6	0	6
Tier 3	0	0	0
Total	81	443	524

In Wales, PFBS was the most prevalent species in raw water during 2024 which was present in 23 tests (28% of total PFAS detections above the limit of detection). In Wales, the most prevalent species in treated water was also PFBS, being present in 42% of tests with detections above LoD (216 in number). The table below sets out all the other parameters which contributed greater than 1% of detections by number of samples rather than by result for all tiers in raw water. This includes the ’sum of PFAS’ parameter. For reference a total of 329,192 tests were undertaken on raw water samples in England, and 12,113 in Wales, in order to produce these results.

Where PFAS is identified, action is taken by the companies in line with the risk prioritisation strategy. In 2024, there were no detections in Wales within tier 2 and 3 in final treated water. Dŵr Cymru Welsh Water had a detection within tier 2 from Llechryd works in April 2024, however as part of the company’s investigation, it was determined that the result was a false positive due to an error within the laboratory testing process. Actions were identified to prevent a reccurrence.

Table 12 Raw water tests Wales and England (greater than limit of detection)

Wales	Tier 1 Detections	Tier 2 Detections	Total	England	Tier 1 Detections	Tier 2 Detections	Tier 3 Detections	Total
PFBS	23		23	PFOS	1499	541	74	2,114
PFBA	18	1	19	PHFHxS	1254	428	25	1,707
PFOA	10	1	11	PFOA	1603	93	7	1,703
PFHxA	3	1	4	PFHxA	1405	197	15	1,617
11Cl-PF3OUdS	3		3	PFBS	1476	49	2	1,527
PFUnDA	3		3	PFBA	1223	46		1,269
PFDoDA	2		2	PFPA	821	200	15	1,036
PFDS	2		2	PFHpA	883	10	14	907
PFHpA	1	1	2	PFecHS	216	122		338
4:2 FTSA	1		1	PFPS	264	32	3	299
6:2 FTSA; 6:2 FTS	1		1	FBSA	206	12	7	225
8:2 FTSA		1	1	6:2 FTAB	189	29	3	221
FBSA	1		1	6:2 FTSA; 6:2 FTS	97	84	13	194
FHxSA		1	1	PFDA	193	1		194
FOSA	1		1	FHxSA	134	49	10	193
MeFOSE	1		1	PFHpS	123	13		136
PFecHS	1		1	8:2 FTSA	115	9		124
PFHpS	1		1	HFPO-TA	115			115
PFNA	1		1	PFNA	115			115
PFOS	1		1	PFUnDA	111			111
PFPS	1		1	EtFOSAA	103			103
Total	75	6	81	MeFOSAA	92			92
				PFNS	92			92
				FOSA	82	9		91
				HFPO-DA (Gen X)	82			82
				PFDS	81			81
				PFDoDA	79			79
				PFHxDA	78			78
				PFODA	78			78
				PFTeA	78			78
				11Cl-PF3OUdS	77			77
				NFDHA	75			75
				EtFOSA	74			74
				PFTrDA	74			74
				4:2 FTSA	72			72
				MeFOSE	72			72
				PFEESA	72			72
				3:3 FTCA	71			71
				DONA	71			71
				PFDoS	71			71
				5:3 FTCA	2		68	70
				PFMOPrA	70			70
				PFMOBA	69			69
				PFUnDS	69			69
				7:3 FTCA	68			68
				MeFOSA	68			68
				EtFOSE	63			63
				9Cl-F3ONS	34			34
				Total	14,059	1,924	256	16,239

Table 13 Treated water tests Wales and England (greater than limit of detection)

Wales	Tier 1 Detections	Total	England	Tier 1 Detections	Tier 2 Detections	Total
PFBS	216	216	PFBA	2,939	75	3,014
PFHxA	47	47	PFHxA	1,943	361	2,304
PFOA	39	39	PFOS	1,493	214	1,707
PFBA	30	30	PFBS	1,489	14	1,503
PFOS	24	24	PFPA	1,058	384	1,442
PFUnDA	13	13	PHFHxS	1,135	167	1,302
PFDA	10	10	PFOA	1,068	57	1,125
9Cl-F3ONS	7	7	PFHpA	698		698
EtFOSAA	7	7	6:2 FTSA; 6:2 FTS	84	367	451
PFNS	6	6	6:2 FTAB	98	8	106
6:2 FTSA; 6:2 FTS	5	5	PFPS	106		106
MeFOSAA	5	5	PFDA	86		86
PFDS	5	5	FBSA	70		70
11Cl-PF3OUdS	3	3	FHxSA	40	22	62
FOSA	3	3	PFHpS	53		53
PFDoDA	3	3	PFecHS	41	8	49
PFNA	3	3	8:2 FTSA	43	1	44
PFPS	3	3	PFNA	36		36
3:3 FTCA	2	2	NFDHA	31		31
EtFOSA	2	2	FOSA	28		28
HFPO-TA	2	2	PFUnDA	27		27
PFHpA	2	2	PFNS	25		25
PFTrDA	2	2	9Cl-F3ONS	22		22
8:2 FTSA	1	1	EtFOSAA	14		14
EtFOSE	1	1	MeFOSAA	14		14
MeFOSE	1	1	PFEESA	14		14
PFUnDS	1	1	PFDoDA	11		11
Total	443	443	PFDS	8		8
			PFTeA	8		8
			11Cl-PF3OUdS	7		7
			HFPO-TA	5		5
			MeFOSE	2		2
			EtFOSA	1		1
			PFHxDA	1		1
			PFMOBA	1		1
			PFODA	1		1
			PFUnDS	1		1
			Total	12,701	1,678	14,379

Table of contents

Table 10 Total number of tests in England including all results less than limit of detection

Table 11 Total number of tests in Wales, not including results less than limit of detection

Table 12 Raw water tests Wales and England (greater than limit of detection)

Table 13 Treated water tests Wales and England (greater than limit of detection)

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Table of contents

Table 10 Total number of tests in England including all results less than limit of detection

Table 11 Total number of tests in Wales, not including results less than limit of detection

Table 12 Raw water tests Wales and England (greater than limit of detection)

Table 13 Treated water tests Wales and England (greater than limit of detection)

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