Water hygiene topic

Disinfection & Chlorination of Mains — for the Blue Card assessment

Swabbing, chlorination, contact time, flushing and sampling before supply.

Practise this in a free mock
Free practice No account needed

Before a new or repaired main carries drinking water it has to be cleaned and disinfected and proven safe. The assessment checks you understand that sequence and why each step matters.

What disinfection and chlorination covers in the assessment

  • A new or repaired main is swabbed to remove debris, then disinfected by chlorination
  • It is dosed to a chlorine concentration and held for a contact time set by the water company's procedure
  • The residual chlorine is checked, then the main is flushed through
  • A bacteriological (water quality) sample is taken and must pass before the main goes into supply
  • Heavily chlorinated water must be de-chlorinated (neutralised) before it is discharged, to protect fish and the environment
  • Disinfection is required whenever a main has been opened, repaired or could have been contaminated

Where people slip up

Putting a repaired main back into supply before the sample has passed.

Discharging super-chlorinated water straight to a stream. It must be neutralised first.

Skipping the swab. Debris left in the main shelters contamination.

Test yourself on disinfection and chlorination

Both free mocks draw from this area — 25 questions in 30 minutes, with an explanation for every answer and a per-area breakdown at the end.

Start a free mock test

The other areas

Why Water Hygiene Matters
Public health and the waterborne diseases that contaminated drinking water can spread.
Personal Health & Hygiene
Weil's disease, reporting illness, hand hygiene and covering cuts.
Contamination: Types & Sources
Microbiological, chemical and physical contamination and where it comes from.
Backflow & Cross-Connection
Back-siphonage, cross-connections and the devices that prevent them.
Hygienic Site Practices
Clean tools and fittings, capping open ends and keeping the trench clean.
Materials & Approved Products
WRAS-approved materials, and the right jointing compounds and lubricants.
Standpipes & Hydrants
Authorised use, backflow protection and keeping them clean.
Working on Live & Repaired Mains
Bursts and repairs, flushing, and returning a main safely to supply.
Legislation & Responsibilities
The Water Industry Act 1991, the Water Fittings Regulations and the DWI.
Read the complete Blue Card guide

Independent study material, not affiliated with or endorsed by EUSR or Energy & Utility Skills. Always check the official EUSR website for the current scheme and card requirements.