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SOP for Out of Acceptance Limit in Purified Water System

To lay down the procedure for actions to be taken in case of out of acceptance limit for critical parameters in the purified water system.

This SOP shall be applicable for purified water generation and distribution systems.


Head of Engineering


Soft Water Hardness
  • If soft water hardness exceeds 5.0 PPM.
  1. Stop the RO system and close the RO inlet valve.
  2. Drain the water from the soft water storage tank.
  3. Check the functioning of the softener unit for regeneration.
  4. Regenerate the softener unit manually and again check the hardness.
  5. If hardness is found within the limit collect the water in the soft water storage tank and restart the RO system.

  • If the pH of the water before RO is found below 7.5, increase the Sodium Hydroxide (NaOH) solution dosing.
  • If the pH of the water before RO is found above 8.0, decrease the Sodium Hydroxide (NaOH) solution dosing.

Pressure drop across micron cartridge filter (MCF)–1 micron
  • If the pressure drop across MCF exceeds 0.8 kg / cm2, replace the MCF.

ORP Value
  • If the ORP value exceeds 350 mv.
  1. Check the free chlorine present in the water at the outlet of the softener (This is checked by Free Chlorine Test Kit).
  2. If it is found more than 2 ppm, reduce the chlorine dosing to get 2 ppm at the outlet of the Softener and follow steps 4 to 7.
  3. If it is 2 ppm, no need to adjust chlorine dosing. Adjust the SMBS dosing to ensure that chlorine is absent before RO.
  4. Stop the soft water pump.
  5. Drain water from the soft water tank.
  6. Collect the fresh soft water in the soft water tank.
  7. Start soft water pump & SMBS dosing.

RO Conductivity
  • In case of RO conductivity exceeds 30 μS / cm.
  1. Check the RO feed water hardness
  2. Check the RO feed water pressure which should not be beyond the limit i.e.5.0 to 9.0 kg/cm2.
  3. Check the port ‘O’ rings of RO membranes.

RO Feed Pressure 5.0 to 9.0 Kg / cm2
  • If the RO feed pressure is found beyond 5.0 to 9.0 kg/cm2.
  1. Check the RO membranes for rupture. If the rupture is found, replace the RO membranes.
  2. Check the RO membranes for fouling. If fouling is found, do the chemical cleaning for RO membranes.

EDI Conductivity
  • If the EDI conductivity exceeds beyond 1.0 μS/cm, Check the EDI feed water conductivity.

Distribution Conductivity
  • If the distribution conductivity exceeds 1.0 μS/cm.
  1. Drain the water from the storage tank.
  2. Drain water from all user points, all sampling points, and pump drain.
  3. Collect the fresh water in the storage tank.
  4. Again check the conductivity of water from the storage tank.
  5. If the conductivity is still higher than the specified limit, do the hot water sanitization of the storage tank and distribution system.

UV Tube Intensity – 2.4 MW / CM2
  • If the UV tube intensity is less than 2.4 MW / cm 2, replace the UV tubes.

SOP: Standard Operating Procedure


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