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Sodium Hypochlorite Dosage for Household and Emergency Water Treatment

Point-of-use  (POU)  water  treatment  with  sodium  hypochlorite  (NaOCl)  has been  proven  to  reduce  diarrheal  disease  in  developing  countries.  However, program  implementation  is  complicated  by  unclear  free  chlorine  residual guidelines  for  POU  water  treatment  and  difficulties  in  determining  appropriate dosage  recommendations.  The  author  presents  evidence  supporting  proposed criteria  for  household  water  treatment  for  free  chlorine  residuals  of  <  2.0  mg/L1  h  after  NaOCl  addition  and  >  0.2  mg/L  after  24  h  of  storage.  In  testing  of  106 drinking  water  sources  from  13  countries,  free  chlorine  residual  was  measured for  24  h  after  treatment  with  different  NaOCl  doses.  For  most  unchlorinated  water(with  turbidity  <  10  ntu  or  from  an  improved  source),  the  NaOCl  dose  necessary to  meet  the  proposed  criteria  was  1.875  mg/L.  For  most  unimproved  sources  with turbidity  of  10–100  ntu,  the  required  dose  was  3.75  mg/L.  POU  chlorination  is  not recommended  in  waters  with  turbidity  >  100  ntu.  The  article  also  discusses  the applicability  of  POU  water  treatment  with  NaOCl  to  emergency  water  treatment.

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