1.2 The Law, the Regulators and Who Must Hold the Card

The Offence: Section 70 of the Water Industry Act 1991

The legal backbone of water hygiene is short enough to state plainly. Under section 70 of the Water Industry Act 1991, where a water undertaker's supply system is used to supply water to premises and that water is unfit for human consumption, the "relevant persons" are guilty of an offence.

Who Can Commit the Offence

The second category of "relevant persons" was inserted by the Water Act 2003, and it is the reason this law matters to you personally. It catches any employer of persons, and any self-employed person, who is concerned in the supply of the water — not just the water company. A contractor working on a main, a self-employed operative making a connection and the firm supplying and fitting materials can all be concerned in the supply. If water is made unfit through that work, those parties can be prosecuted alongside, or instead of, the undertaker.

Illness Is Not Required

The offence is complete when unfit water is supplied. Nobody has to drink it, fall ill or be hospitalised for the offence to have been committed. Illness is evidence of the consequences; supplying the unfit water is the offence itself.

The Defence of Due Diligence

The Act recognises a defence for someone who took all reasonable steps and exercised all due diligence to secure that the water was fit for human consumption on leaving the primary water undertaker's pipes, or that it was not used for human consumption. There is also a defence where the person had no reasonable grounds for suspecting the water would be used for human consumption. For a site worker, due diligence is not abstract — it is the working practice the rest of this guide teaches:

• Following hygiene procedures — disinfecting pipes, fittings and tools; capping or bagging materials; keeping the work area clean
• Health screening — declaring illness and not working on clean water operations while carrying a gastrointestinal illness
• Clean tools and equipment — disinfected gear kept for clean water work, not mixed with dirty or sewage work

If you can show you worked to the trained procedures, you have gone a long way towards the diligence the law expects — and towards preventing the incident in the first place.

The Drinking Water Inspectorate (DWI)

The Drinking Water Inspectorate (DWI) was formed in 1990 to provide independent reassurance that water supplies in England and Wales are safe and that drinking water quality is acceptable to consumers. It is the regulator of drinking water quality: it scrutinises water companies' sampling and treatment, publishes the Chief Inspector's annual report on drinking water quality, and investigates serious incidents. Its June 2026 investigation report into the Brixham outbreak is an example of that incident role.

A Real Consequence: Brixham 2024

The offence in section 70 is not theoretical. After the May 2024 Cryptosporidium outbreak in Brixham, Devon, South West Water pleaded guilty to supplying water unfit for human consumption and on 2 June 2026 was fined a record £1.853 million. There were 143 laboratory-confirmed cases, people were hospitalised, and the boil water notice lasted up to eight weeks for some households. We use this here only as evidence that the offence is enforced in practice — a fuller case study of the incident appears later in this guide.

Who Does What

Restricted Operations is the industry's term for work where hygiene matters most: entering clean water sites and working on the clean water network. The National Water Hygiene scheme was developed in collaboration with all UK water companies, which is why one registration is recognised across the industry.

Who Must Hold the Card

Note the logic: registration attaches to the work and the place, not to who employs you. A subcontractor's operative laying a main and an SLO's engineer making a connection need the same registration as the water company's own staff, and a supervisor entering a covered storage site to inspect the work needs it too. Water UK's Principles of Water Supply Hygiene add that visitors to treatment works should be strictly supervised and kept out of areas of restricted operation: escorting is the control for people who do not hold the card.

Related Law You Will Meet Later

The fittings side of the law — the Water Supply (Water Fittings) Regulations 1999 (SI 1999/1148), in force on 1 July 1999, which govern water fittings in England and Wales — is pointed to here for completeness and taught in Chapter 8 of this guide.

Common Candidate Traps

• "Only the water company is liable." Since the Water Act 2003, employers and self-employed people concerned in the supply are relevant persons too — contractors can commit the offence.
• "The card is optional for subcontractors." UK water companies require anyone entering clean water sites or working on the clean water network to be registered, including subcontractor staff and SLO personnel.
• "Section 70 needs actual illness." Supplying water unfit for human consumption is the offence; illness is not an element of it.