BS 8558: what the water supply hygiene standard covers
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Key points
- BS 8558 is a guide, not a law. It helps you design and run water systems hygienically, but following it does not, on its own, discharge your legal legionella duty.
- The current version is BS 8558:2015. It replaced BS 8558:2011, which had already taken over guidance from the withdrawn BS 6700.
- "Domestic use" means water used for drinking, cooking, washing and sanitary purposes in any building, including offices, schools and care homes. It is not limited to houses.
- BS 8558 complements the European BS EN 806 series. BS EN 806 sets the requirements; BS 8558 fills the UK-specific gaps such as backflow fluid categories, storage and temperature.
- It sits alongside, not instead of, BS 8580 (legionella risk assessment) and ACOP L8 and HSG274 (the HSE legal framework).
BS 8558 is the British Standard guiding the hygienic design, installation, testing and maintenance of water services supplying water for domestic use inside buildings. The current edition, BS 8558:2015, gives UK-specific guidance that complements the BS EN 806 series and, together with BS EN 806, took over the design guidance from the withdrawn BS 6700.
What BS 8558 actually is
BS 8558 is a British Standard published by BSI. Its full title is a guide to the design, installation, testing, operation and maintenance of services supplying water for domestic use within buildings and their curtilages. The word guide matters. BS 8558 is guidance, written in terms of what you should do, rather than a specification written in terms of what you shall do.
That distinction sets its place in the standards hierarchy. The specification for water installations inside buildings is the European BS EN 806 series. BS 8558 was written to sit on top of that series and add the UK-specific detail the European standard leaves out, because BS EN 806 has to work across many countries with different plumbing regulations. So BS 8558 is best read as the UK companion to BS EN 806, not a standalone rulebook.
The current edition is BS 8558:2015. It is a design and engineering document aimed at anyone specifying, installing, commissioning or maintaining hot and cold water services, from architects and plumbers to facilities and water-hygiene teams.
What BS 8558 covers
BS 8558 runs across the whole life of a water service, from the incoming main to the point of use. The main areas it gives guidance on are:
- Materials and fittings. Selecting fittings that will not taint or contaminate the water, in line with the Water Supply (Water Fittings) Regulations and the fittings approval scheme.
- Pipe sizing. Sizing pipework using loading units so that outlets deliver enough flow without oversizing runs, which would slow turnover and encourage stagnation.
- Backflow prevention. Protecting the supply against backflow using the fluid risk categories, complementing BS EN 1717.
- Water storage. Designing cold water storage cisterns and hot water storage so water turns over, stays covered, and does not sit warm and stagnant.
- Avoiding dead legs and stagnation. Keeping branch pipework as short as possible and designing out little-used sections, because standing water is where problems start.
- Commissioning. Pressure testing, flushing out debris, and disinfecting new or altered pipework, including the chlorination procedures used before a system is handed over.
- Temperature and insulation. Keeping hot water hot, cold water cold, and lagging pipes so the two do not warm or cool each other.
Read together, these are the design measures that keep water moving, keep it out of the temperature range bacteria prefer, and keep it clean from the day the system is commissioned.
| Document | Type | What it does | Status |
|---|---|---|---|
| BS 8558:2015 | Guide (guidance) | UK guidance on hygienic design, installation, testing and maintenance of water services for domestic use | Current, replaced BS 8558:2011 |
| BS EN 806 (parts 1 to 5) | Specification (requirements) | European requirements for installations conveying water for human consumption inside buildings | Current |
| BS EN 1717 | Specification | Protection against backflow and contamination, using fluid risk categories | Current |
| BS 6700 | Former UK standard | Old UK design and installation standard for water supply | Withdrawn, split into BS EN 806 and BS 8558 |
| BS 8580-1 | Code of practice | How to carry out a legionella risk assessment | Current |
| ACOP L8 and HSG274 | Approved Code of Practice and HSE guidance | The legal duty to assess and control legionella, and how to meet it | Current |
British Standards Institution and HSE guidance
"Domestic use" does not mean domestic buildings
The single most common misconception about BS 8558 is that it only applies to homes. The title says "water for domestic use", and people read that as "water in houses". It does not mean that.
"Domestic use" describes how the water is used, not the type of building it is used in. Water for domestic use is water for drinking, cooking, washing and sanitary purposes, as opposed to water for an industrial process or firefighting. That kind of water is used in almost every building there is.
So BS 8558 applies to the domestic water services in an office, a school, a hotel, a care home or a hospital just as much as in a house. If a building has taps, showers, toilets and a supply of wholesome water, the design guidance in BS 8558 is relevant to it. Treating the standard as a domestic-only document is how genuine risks in commercial and public buildings get overlooked.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
Follows ACoP L8 and HSG274 Part 2. Free. No spam.
BS 8558:2011, BS 8558:2015 and the end of BS 6700
If you have seen the standard quoted as BS 8558:2011, that is the first edition. BS 8558 was first published in 2011 to take over the design guidance that used to live in BS 6700, the long-standing UK standard for water supply, cistern and distribution systems.
What happened to BS 6700 is worth understanding, because it explains why two standards now cover ground one used to. BS 6700 was withdrawn. Its content was split in two: the requirements moved into the European BS EN 806 series, and the UK-specific complementary guidance moved into BS 8558. So a reference to BS 6700 in an old specification should now be read as BS EN 806 plus BS 8558.
BS 8558 itself was then updated, and the current edition is BS 8558:2015. If a document, method statement or supplier quotes BS 8558:2011, it is citing the superseded edition. The 2015 version is the one to work to.
How BS 8558 fits with BS EN 806, BS 8580 and ACOP L8
BS 8558 is one document in a family, and it is easy to blur what each one does. Keeping them separate matters, because they answer different questions and only one of them carries the legal duty.
- BS EN 806 is the specification. It sets the requirements for installations conveying water for human consumption inside buildings.
- BS 8558 is the UK guide that complements BS EN 806 and tells you how to meet those requirements in a British context.
- BS 8580 is the code of practice for how to carry out a legionella risk assessment. It is a method for assessing risk, not a design guide.
- ACOP L8 and HSG274 are the HSE Approved Code of Practice and technical guidance. They carry the legal duty, under health and safety law, to assess and control the risk of legionella.
Designing a system to BS 8558 removes many of the conditions legionella needs, so it makes the risk-assessment job easier and the system safer by design. What it does not do is replace the risk assessment or the legal duty. You can install pipework fully to BS 8558 and still be required, under ACOP L8, to assess the finished system, write a scheme to control it, and keep records. BS 8558 is a design standard; the duty to manage the live system is separate.
Where BS 8558 meets your legionella duty
The overlap between BS 8558 and day-to-day legionella control is at three points, and they are the same three the HSE technical guidance in HSG274 keeps returning to: temperature, stagnation and cleanliness.
Temperature. BS 8558 sits behind the temperature regime the HSE expects. Cold water should be stored and distributed below 20°C, because 20°C to 45°C is the range in which legionella grows. Hot water should be stored at 60°C and reach the tap at 50°C, or 55°C in healthcare premises. Getting the design right, insulation, pipe routing and storage, is what makes those figures achievable once the building is in use.
Stagnation. The guidance on sizing pipework and avoiding dead legs is legionella control by design. Water that keeps moving does not give the bacteria time to establish. This is where the standard and the risk assessment meet most directly, because a dead leg designed out at installation is one you never have to flush or record later.
Commissioning. The flushing and chlorination procedures in BS 8558 matter because a system that is left full of static water between installation and occupation can be contaminated before anyone uses it.
None of this proves a system is safe. It shows where the design should have removed risk, and where your risk assessment then has to check that it actually did. The findings, and the flushing and temperature records that follow, belong in the written risk assessment and the written scheme of control. Our free template has sections for exactly that.
BS 8558 is a guide, not a law. Designing to it helps you avoid the conditions legionella needs, but it does not, on its own, discharge your duty under ACOP L8 to assess and control the risk.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
Follows ACoP L8 and HSG274 Part 2. Free. No spam.
Frequently asked questions
What is the BS 8558 water regulation?
BS 8558 is not a regulation. It is a British Standard, and specifically a guide, so it carries guidance rather than the force of law. The statutory requirements for water fittings and supply come from the Water Supply (Water Fittings) Regulations 1999 in England and Wales, and the equivalent byelaws in Scotland. BS 8558 gives practical guidance that helps you meet those regulations and the requirements of BS EN 806. For legionella specifically, the legal duty comes from health and safety law, set out in the Approved Code of Practice ACOP L8. Following BS 8558 supports compliance but is not, by itself, a legal requirement.
Is BS 6700 still current?
No. BS 6700 has been withdrawn. Its content was split in two when it was superseded: the requirements moved into the European BS EN 806 series, and the UK-specific complementary guidance moved into BS 8558. If a specification, drawing or method statement still references BS 6700, it should be updated to cite BS EN 806 and BS 8558:2015 instead.
What is BS EN 806?
BS EN 806 is the European standard series, adopted in the UK, that specifies requirements for installations inside buildings conveying water intended for human consumption. It runs to five parts covering general matters, design, pipe sizing, installation, and operation and maintenance. It sets the requirements; BS 8558 is the UK guide that complements it and explains how to meet those requirements in a British context.
What is the British Standard for water?
There is no single British Standard for water. For water services inside buildings the two key documents are BS EN 806, which sets the requirements, and BS 8558, which gives the UK complementary guidance. For assessing legionella risk the standard is BS 8580. For protecting the supply against backflow it is BS EN 1717. Which one applies depends on whether you are designing, installing, or assessing the risk of a system.
Does BS 8558 apply to commercial buildings?
Yes. The phrase "water for domestic use" in the title refers to how the water is used, for drinking, cooking, washing and sanitary purposes, not to the type of building. BS 8558 applies to the domestic water services in offices, schools, hotels, care homes and hospitals just as much as in houses. Any building with a supply of wholesome water and normal taps, showers and toilets falls within its scope.
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