Contamination is covered by The Regulations.

See Regulations 3 and 4

It can occur in one of the following ways:

  1. By unsuitable materials or substances.
  2. By backsiphonage, backflow or cross connection.
  3. By incorrectly stored water.
  4. By unsuitable or incorrectly installed water fittings.
  5. By sanitary appliances and draw off taps.
  6. By other associated (related) building services.

Please find a pictorial explanation of backsiphonage in this section.

For other examples please contact your tutor.


Normal Operation
Initially:
  • Taps A and B, and valve C are closed
    and cistern is full.
  • Stopvalve D is open.
  • Water is static.

Normal Operation of Indirect Services

  • Tap A is opened.
  • Valve C opens.
  • Pressure in the water main causes water to flow upwards through stopvalve D.
  • Tap A is closed and the cistern re-fills.

Normal Operation of Direct Cold Water

  • Tap B, for drinking water, is opened.
  • Pressure in the water main causes water to flow upwards through stopvalve D.



 

Abnormal Operation

Contamination can occur as a result of 'Back-Siphonage'.

Stage 1

  • If valve C is faulty and does not close :-
  • water will continue filling the cistern, immersing the valve, until (hopefully) the stop-valve D closes.

Stage 2 - Contamination Occurs

  • Tap B is opened for drinking water.
  • Siphonic action displaces cistern water through potable water outlet.

Contamination of Water Main

  • If the stopvalve D remains open in stage 1 and a pressure drop occurs in the water main :-
  • water held in the cistern is displaced and siphoned into the drinking water main.