Pond Liner for Drinking Water Reservoirs UK — Potable Water Compliance Guide

Lining a drinking water reservoir, raw water storage pond, or potable water supply structure in the UK requires a liner specification that meets stringent regulatory and material standards. This guide covers the key compliance requirements for geomembrane liners in contact with drinking water.

Regulatory Framework

WRAS — Water Regulations Advisory Scheme

The Water Regulations Advisory Scheme (WRAS) assesses and certifies products used in contact with potable water in the UK. WRAS approval demonstrates that a material complies with BS 6920 and does not adversely affect the taste, odour, colour, or safety of water. For any pond liner used in a drinking water application, WRAS-approved products should be specified wherever available.

NSF/ANSI 61 — Drinking Water System Components

NSF 61 is the internationally recognised standard for materials in contact with drinking water. It covers the migration of contaminants, taste, odour, and water quality impacts. HDPE geomembranes manufactured to NSF 61 standards are the preferred choice for potable water reservoirs. This standard is widely referenced in UK water industry specifications alongside WRAS.

BS 6920 — Suitability of Non-Metallic Products in Contact with Water for Human Consumption

BS 6920 is the UK standard against which WRAS testing is conducted. Products tested to BS 6920 are assessed for: (i) effect on taste and odour; (ii) cytotoxicity; (iii) mutagenicity; (iv) growth of aquatic micro-organisms; (v) extraction of metals; (vi) extraction of organic compounds.

DWI — Drinking Water Inspectorate

The DWI regulates public water supplies in England and Wales. Water companies are required under the Water Industry Act 1991 to supply wholesome water meeting the standards in the Water Supply (Water Quality) Regulations 2016. Materials used in contact with potable water must not compromise water quality, and water companies typically require WRAS or equivalent approval for all materials.

HDPE for Potable Water Applications

HDPE geomembrane is the material of choice for drinking water reservoirs because:

• It is completely inert — no plasticisers, no leachable compounds under normal service conditions
• It can be manufactured to NSF 61 standards with appropriate carbon black and resin grade
• Welded seams eliminate the chemical-based adhesives required for EPDM and butyl jointing
• Long design life (40–60 years in potable water service)
• Resistance to chlorine and chloramines used in water treatment

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The UK Regulatory Framework for Drinking Water Reservoir Liners

Water Industry Act 1991 and the Drinking Water Inspectorate

The Water Industry Act 1991 establishes the legal framework under which water companies in England and Wales supply drinking water. The Drinking Water Inspectorate (DWI) is the independent regulator responsible for monitoring and reporting on the quality of drinking water supplied by water companies. The DWI sets the standards that materials in contact with drinking water must meet, issues Regulations 31 approvals for new water treatment and storage materials, and investigates incidents affecting drinking water quality.

Any material used in a UK drinking water reservoir or storage structure — including geomembrane liners — must satisfy the DWI's requirements. Failure to use approved materials can result in enforcement action, including requirement to drain and reline the structure at significant cost.

Water Supply (Water Quality) Regulations 2016

The Water Supply (Water Quality) Regulations 2016 (as amended) implement the EU Drinking Water Directive 98/83/EC in England (parallel regulations apply in Wales, Scotland, and Northern Ireland). Regulation 31 requires that:

• Products and materials in contact with water intended for human consumption do not compromise water quality
• Only approved products and materials are used in new installations or when replacing existing installations
• Water companies maintain records of materials used in their infrastructure

Compliance with Regulation 31 is demonstrated through product approval schemes — principally WRAS (Water Regulations Advisory Scheme) approval in the UK.

WRAS Approval: The BS 6920 Test Battery

WRAS (Water Regulations Advisory Scheme) operates the UK's primary product approval scheme for materials in contact with drinking water. WRAS approval is based on testing to BS 6920:2014 ("Suitability of non-metallic materials and products for use in contact with water intended for human consumption with regard to their effect on the quality of the water"). The BS 6920 test battery covers:

Test	Requirement
Taste and odour	Taste threshold factor <3; no taint at normal use concentration
Appearance (turbidity, colour)	No perceptible change compared to control water
Microbiological growth promotion	Biomass formation ratio ≤1.0; no selective stimulation of specific organisms
Cytotoxicity	Test extract must not be cytotoxic to mammalian cells in culture
Mutagenicity (Ames test)	No mutagenic activity detected
Metals (ICP analysis)	Concentrations below respective parametric values in Reg 31 or specific DWI guidance
Organic compounds (GC-MS)	Individual organics below 1 µg/l; total organics below 10 µg/l in test extracts

HDPE geomembrane manufactured from approved resins routinely passes all BS 6920 test requirements. WRAS-approved HDPE liners carry the WRAS logo and a product approval reference number, which should be provided to the DWI as part of any new reservoir regulatory submission.

Approved HDPE Resins for Potable Water Contact

Not all HDPE geomembrane is suitable for potable water contact — the resin formulation, including any carbon black or colouring compounds, antioxidant additives, and processing aids, must be approved. Leading geomembrane manufacturers whose products are WRAS-approved or carry equivalent European (DVGWand KIWA) potable water contact approvals include:

• GSE Environmental (GSE HD Potable Grade)
• Solmax (Solmax 60PT potable series)
• AGRU (AGRU PE 100-RC HS potable grade)
• Atarfil (AT-30 potable water series)

Always request the specific WRAS approval certificate (not just a claim of approval) and verify the approval reference number on the WRAS database at wras.co.uk/product-approvals before accepting delivery of material for a potable water project.

Geomembrane vs Concrete Lining: Cost Comparison for Water Supply Reservoirs

Two principal lining approaches are used for UK drinking water reservoirs and raw water storage ponds:

Factor	HDPE Geomembrane	In-situ Concrete
Capital cost (new construction, per m²)	£18–£35/m² supplied and installed	£80–£150/m² (depending on thickness and reinforcement)
Relining existing structures (per m²)	£22–£45/m²	£90–£180/m² (breaking out existing and recasting)
Design life	40–80 years (depending on specification)	30–50 years (subject to crack repair)
Seepage rate	Effectively zero (10⁻¹³ m/s)	Low but not zero (cracking, joint failure)
Repair methodology	Patch welding or adhesive repair; no plant shutdown required in most cases	Concrete repair, recoating; typically requires full dewatering
Construction programme	Fast (large panels, minimal curing)	Slow (formwork, pour, cure, waterproof)
Potable water compliance	WRAS-approved HDPE is compliant	Concrete with approved coating is compliant

HDPE in the UK Water Industry

HDPE geomembrane is well-established in UK water industry infrastructure:

• Raw water storage reservoirs at upland treatment works have been lined with HDPE since the 1990s, with early UK installations now exceeding 25 years in service
• Treated water storage (covered service reservoirs) increasingly use HDPE floating covers and base liners
• Leakage prevention programmes at water company sites often include HDPE lining of leaking reservoir bases and embankments
• Thames Water, Yorkshire Water, Anglian Water, and other major water companies have used HDPE geomembrane in both raw and treated water storage applications

Enhanced Liner Testing for Potable Water Applications

For potable water reservoirs, liner testing requirements exceed standard geomembrane construction quality assurance (CQA). Additional requirements typically specified by water companies and the DWI include:

• Weld testing: 100% non-destructive testing of all seams (vacuum box test or air pressure test for HDPE double-wedge welds); minimum 1% destructive peel and shear testing
• Batch traceability: Full material traceability from polymer resin through to installed liner, with certificates of conformity at each stage
• Third-party CQA: Independent CQA inspector (not employed by the installer) present during all welding operations
• Pre-installation water test: Representative liner panel immersed in potable water for 72 hours; water tested to Regulation 31 parametric values before installation proceeds
• Post-installation flood test: Where feasible, reservoir filled with clean water and held for 48 hours to confirm zero seepage before connection to supply

Water Treatment Chemical Compatibility

HDPE geomembrane for potable water reservoirs must be compatible with the full range of water treatment chemicals used in the supply system:

Chemical	Typical Concentration	HDPE Compatibility
Free chlorine (disinfection)	0.1–1.0 mg/l	Excellent — no effect at potable concentrations
Chloramine (combined chlorine)	0.5–3.0 mg/l	Excellent — HDPE is preferred over EPDM for chloramine resistance
Aluminium sulphate (coagulation)	Dosed upstream, residual in water	Excellent
Ferric sulphate (coagulation)	Dosed upstream, residual in water	Excellent
pH adjustment (H₂SO₄, NaOH)	pH 6.5–9.0 final	Excellent — HDPE stable across pH 2–14
Fluoride dosing	Up to 1.0 mg/l	Excellent

Important note on EPDM: Standard EPDM rubber liners show significantly lower resistance to chloramine compared to HDPE. For chloraminated supply zones, HDPE is strongly preferred for all potable water contact applications.

Liner Leaching: HDPE Extraction Data

Independent extraction studies on HDPE geomembrane in contact with potable water consistently show:

• Heavy metals (lead, cadmium, chromium, nickel, etc.): below detection limits in all studies
• Organic compounds (individual): typically <0.1 µg/l in extraction tests — well below the 1 µg/l Regulation 31 limit
• Total organics: typically <2 µg/l — well below the 10 µg/l Regulation 31 limit
• No endocrine-disrupting compounds detected in peer-reviewed studies of HDPE geomembrane water contact extracts

These data support HDPE's status as the preferred geomembrane material for potable water contact applications in the UK and internationally.

DWI Regulatory Submission for New Lined Reservoirs

Water companies are required to notify the DWI before commissioning new storage reservoirs or significantly modifying existing ones. The submission package for a HDPE-lined reservoir typically includes:

• WRAS product approval certificate for the specified liner material
• Third-party CQA records including welder qualification certificates, weld test results, and material certificates of conformity
• As-built drawings showing liner layout, seam locations, and anchor trench details
• Post-installation flood test results
• Operational and maintenance plan for the liner

Renewal and Relining of Existing Reservoirs

Many UK water industry reservoirs constructed in the 1960s–1990s are reaching the end of their design life or have developed seepage issues. HDPE relining of existing structures offers significant advantages over reconstruction:

• The existing structure (embankment, concrete base, brick walls) provides substrate for the new liner, reducing civil engineering costs
• Reservoir is out of service only for the lining installation period (typically 4–12 weeks for a medium reservoir) rather than the 12–24 months required for reconstruction
• Proven technique with 30+ year track record in the UK water industry

Pre-relining inspection by a qualified structural engineer is essential to confirm that the existing structure is sufficiently sound to support the new liner without risk of differential settlement or structural failure.

Emergency Procedures for Liner Damage in Operational Reservoirs

Despite the durability of HDPE geomembrane, damage can occur from:

• Vandalism (including deliberate cutting)
• Animal burrowing or root penetration at the liner edges
• Settlement-induced seam stress in poorly designed installations
• UV degradation in uncovered sections (for open reservoirs)

Emergency response protocol for a damaged reservoir liner:

1. Isolate the reservoir from supply and notify the DWI if water quality is potentially compromised
2. Locate the damage using electrical leak detection (ELD) survey — specialist contractors can identify leak locations to within 1m accuracy without dewatering
3. Assess whether in-water repair is feasible (for small punctures <50mm) using underwater HDPE repair patches and approved adhesive
4. For seam failures or large damage areas, drain the reservoir, dry the liner surface, and undertake thermal or extrusion weld repair under CQA supervision
5. Retest repaired area and document for DWI records

Whole-Life Cost Analysis: HDPE vs Concrete (100-Year Horizon)

A whole-life cost analysis over a 100-year planning horizon strongly favours HDPE geomembrane over concrete for water storage reservoir lining:

Cost Element	HDPE (100 years)	Concrete (100 years)
Initial installation	1× base cost	3–4× base cost
Planned replacement (liner)	1 replacement at ~60 years	2–3 major repairs/overlays
Unplanned repairs	Low — patch welding	Higher — concrete cracking common
Seepage losses (operational)	Effectively nil	0.5–2% annual loss possible
Regulatory compliance cost	WRAS-approved products streamline approval	Comparable if approved coating used
Net present cost (whole life, relative)	1.0	2.2–3.5

Ready to Specify a WRAS-Approved Pond Liner for Your Reservoir?

Our team supplies WRAS-approved HDPE geomembrane for drinking water reservoir applications across the UK. We work with water companies, local authorities, and private water supply operators to specify the correct material and provide the documentation package required for DWI regulatory submissions.

Browse our WRAS-approved pond liner range or contact our technical team for expert advice on potable water liner specification.