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Sodium Hypochlorite Dosage for Household and Emergency Water Treatment: Updated Recommendations

Household  water  treatment  with  chlorine  can  improve  the  microbiological  quality  of  household  water and  reduce  diarrheal  disease.  We  conducted  laboratory  and field  studies  to  inform  chlorine  dosage recommendations.  In  the  laboratory,  reactors  of  varying  turbidity  (10–300  NTU)  and  total  organic carbon  (0–25  mg/L  addition)  were  created,  spiked  with Escherichia  coli,  and  dosed  with  3.75  mg/Ls odium  hypochlorite.  All  reactors  had>4  log  reduction  of E.  coli 24  hours  after  chlorine  addition. In  the field,  we  tested  158  sources  in  22  countries  for  chlorine  demand.  A  1.88  mg/L  dosage  for  water from  improved  sources  of<5  or<10  NTU  turbidity  met  free  chlorine  residual  criteria  (2.0  mg/L  at 1  hour,0.2  mg/L  at  24  hours)  91–94%  and  82–87%  of  the  time  at  8  and  24  hours,  respectively.In  unimproved  water  source  samples,  a  3.75  mg/L  dosage  met  relaxed  criteria  (4.0  mg/L  at  1  hour,0.2  mg/L  after  24  hours)  83%  and  65%  of  the  time  after  8  and  24  hours,  respectively.  We recommend  water  from  improved/low  turbidity  sources  be  dosed  at  1.88  mg/L  and  used  within 24  hours,  and  from  unimproved/higher  turbidity  sources  be  dosed  at  3.75  mg/L  and  consumed  within 8  hours.  Further  research  on field  effectiveness  of  chlorination  is  recommended.

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