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Well Disinfection Systems with NaDCC Tablets

After the construction of a well and installation of the pump, laying of mains and service pipework, or the building of a water storage structure, or if biological pollution has entered the water system, then the system should immediately be disinfected to kill any microorganisms present.

Wells/Tubewells

  1. 10 x 8.68g NaDCC tablets are dissolved in 50 litres of water in an open area.
  2. Half the solution is poured into the well and the pump operated until the water pumped out (or from all the opened taps in a household) distinctly smells of chlorine.
  3. The pumping is stopped, and the rest of the solution poured down the well.
  4. After waiting one hour, water is pumped again (with all the taps in the household open) for several minutes.
  5. The pumping is stopped and the system left for at least twelve hours
  6. At the end of this time, the water is pumped to waste until the residual chlorine level is <2mg/l (2ppm)
  7. The system is then re-filled with potable water

Spring Boxes or Silt Traps

  • 10 x 8.68g NaDCC tablets are dissolved in 50 litres of water in an open area.
  • The inside walls are scrubbed with the solution, especially between the water level and the highest point the water level may reach, using half the solution.
  • The rest of the solution is poured into the well/box/trap.
  • In the case of a pump facility the procedures 4), 5), 6) and 7) above are followed.
  • The water is run to waste to leave a residual chlorine level of < 2mg/l (2ppm)
  • The system is re-filled with potable water.

Mains Pipe Disinfection

  • 1 x 8.68g NaDCC tablet per 100 litres are made up in sufficient water to enter the mains pipework at the charging point, to fill the entire system
  • The system is left for at least 24 hours. All the valves are operated at least once during this period, to disinfect the fittings, valves, hydrants etc.
  • Residual chlorine levels are taken at the point furthest from the charging point. Disinfection is repeated until this residual chlorine level is > 10 mg/l (10 ppm).
  • After disinfection, the water is flushed out of the system to leave a residual chlorine level of < 2 mg/l (2 ppm).
  • The system is re-filled with potable water

Service Pipe Disinfection

  • 1 x 8.68g NaDCC tablet per 333 litres are made up in sufficient water to enter the service pipes.
  • Once completely filled, the pipelines are closed and left for at least 24 hours.
  • After disinfection the water is flushed out of the system to leave a residual chlorine level of < 2 mg/l (2 ppm).
  • The system is re-filled with potable water.

Water Structure Disinfection

  • 1 x 8.68g NaDCC tablet per 250 litres are made up in sufficient water to disinfect the water structure.
  • The solution is distributed over the floor of the structure to a depth of 300mm.
  • This solution is also used to spray soffits, walls, columns etc., to ensure that all exposed areas are covered.
  • After disinfection all the water is flushed out to waste.
  • The system is then re-filled with potable water.

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