Disinfection of Water Systems Quiz

Under what circumstances is disinfection of large cold water systems required?

• Only during new installations in single-family homes

• When the system is suspected of contamination

• For underground pipework installations

• Where the system has not been in regular use nor regularly flushed

• Where no large extensions or alterations to systems have been undertaken

What is the initial concentration of the disinfection agent required?

• 30ppm

• 50ppm

• 100ppm

• 200ppm

How long should chlorinated water stand within the pipework during disinfection?

• 30 minutes

• 1 hour

• 2 hours

• Overnight

What is the required free residual chlorine content at the furthest outlet after the disinfection process?

• 10ppm

• 20ppm

• 30ppm

• 40ppm

What safety measure is NOT recommended during the disinfection process?

• Wearing PPE such as goggles and aprons

• Using household bleach as a disinfectant

• Avoiding chemical contact with other chemicals

• Consulting COSHH data sheets

How is the capacity (in litres) of a cistern calculated?

• Radius(m) × π × height(m) to water line × 1,000

• Length(m) × Width(m) × Height(m) to water line × 1,000

• Length(m) × Width(m) × Radius(m) × 1,000

• Volume ÷ 1,000

If a pipe has a diameter of 150mm and a length of 11m, what is its capacity in litres?

• 194.41 litres

• 0.194 litres

• 4.84 litres

• 5.84 litres

What ratio of sodium hypochlorite solution to water creates a 50ppm concentration?

• 1 litre to 500 litres
• 1 litre to 250 litres

• 1 litre to 1000 litres

• 1 litre to 750 litres

What should be done before draining heavily chlorinated water?

• Neutralize with sodium thiosulphate

• Add more chlorine

• Flush immediately into a watercourse

• Mix with household chemicals

Which of the following is a DO NOT instruction for disinfection?

• Warn people before starting disinfection

• Leave water in the system for more than an hour

• Check chlorine levels after the test period

• Use chlorinated water to maintain levels during testing