Tubewells are contaminated during construction mainly due to the use of contaminated surface waters for sinking. Sometimes contaminating materials are used to stabilize the bore hole against collapse and caving. Tubewells in Bangladesh are also contaminated due to submergence in flood or under storm surges. The contaminated tubewells need disinfection by the following procedure:
a. Prepare about 50 l of chlorine solution with a chlorine concentration of 50 mg/l (dissolved 0.150 gms of bleaching powder containing 33% chlorine in 1 liter of water).
b. Open the base of the tubewell and pour the chlorine solution in the pipe slowly. The chlorine solution will fill the pipe and then enter into the aquifer through the strainer.
c. Dismantle the tubewell and submerge/wash smaller components in the chlorine solution and wipe all the surfaces of larger components with the same chlorine solution. Then reassemble and fix the tubewell.
d. Wait for at least six hours and than pump out the water until traces of chlorine can be smelled in water produced by the tubewell.
e. When the pumping of the tubewell is completed, the disinfected tubewell is ready for regular use.