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System Operation: Record Keeping


In order to be able to follow the performance of the RO unit, it is necessary that all relevant data are collected, recorded and kept on file. Apart from keeping track of the performance, the logsheets are also valuable tools for troubleshooting, and are needed in the cases of warranty claims.

This instruction is for general guidance only and must not be used in place of the operating manual for a particular plant. Site-dependent factors prevent specific recommendations for all record keeping. Thus, only the more general record keeping is covered here.

Start-Up Report

  • Provide a complete description of the RO plant. This can be done using a flow diagram and equipment, instrumentation, and material list to show water source, pretreatment system, RO configuration and post-treatment system.
  • Give results of checking according to check list (Pre-Start-up Check and Commissioning Audit)
  • Provide calibration curves of all gauges and meters based on manufacturers' recommendations.
  • Record initial performance of RO and pretreatment system as provided below.

RO Operating Data

The following data must be recorded and logged into an appropriate logsheet at least once per shift, unless otherwise stated.
Use this sample
RO Operating Log as an example.

  • Date, time and hours of operation.
  • Pressure drop per filter cartridge and per stage.
  • Feed, permeate and concentrate pressure of each stage.
  • Permeate and concentrate flows of each stage.
  • Conductivity of the feed, permeate and concentrate streams for each stage. Permeate conductivity of each pressure vessel weekly.
  • TDS of feed, permeate and concentrate streams for each stage. The TDS is calculated from the water analysis.  It can also be calculated from the conductivity (at 25°C) EC25 and an appropriate K factor:
    TDS = K EC25

    The K factor has to be determined for each specific stream. Typical K factors are shown in
    Table 1 Below.
  • pH of the feed, permeate and concentrate streams.
  • Silt Density Index (SDI) or turbidity of the RO feed stream, or both.
  • Water temperature of the feed stream.
  • Langelier Saturation Index (LSI) of the concentrate stream from the last stage (for concentrate streams < 10,000 mg/l TDS).
  • Stiff and Davis Stability Index (S&DSI) of the concentrate stream from the last stage (for concentrate streams >10,000 mg/l).
  • Calibration of all gauges and meters based on manufacturer’s recommendations as to method and frequency but no less frequent than once every three months.
  • Any unusual incidents, for example, upsets in SDI, pH and pressure and shutdowns.
  • Complete water analysis of the feed, permeate and concentrate streams and the raw water at start-up and every week thereafter.

    The water analysis shall include:
    • Calcium
    • Magnesium
    • Sodium
    • Potassium
    • Strontium
    • Barium
    • Iron (total, dissolved and ferrous)
    • Aluminium (total and dissolved)
    • Bicarbonate
    • Sulfate
    • Chloride
    • Nitrate
    • Fluoride
    • Phosphate (total)
    • Silica (dissolved)
    • Total dissolved solids
    • Conductivity
    • pH
    • TOC

Pretreatment Operating Data

Since the RO system performance depends largely on the proper operation of the pretreatment, the operating characteristics of the pretreatment equipment should be recorded. Specific recommendations for all record keeping cannot be given, because pretreatment is site dependent. Typically, the following items must be recorded:

  • Total residual chlorine concentration in the RO feed (daily - unless known to be completely absent).
  • Discharge pressure of any well or booster pumps (twice a day).
  • Pressure drop of all filters (twice a day).
  • Consumption of acid and any other chemicals (daily - if used).
  • Calibration of all gauges and meters based on manufacturers' recommendations as to method and frequency but no less frequent than once every 3 months.
  • Any unusual incidents, for example, upsets and shutdowns as they occur.


                                                                                FEED ANALYSIS










As Ion












Ca ++
















Mg ++
















Na ++
















K +
















Fe ++










































Calculate the total cations and total anions as calcium carbonate.  If the difference between the two

totals is less than 10%, the analysis is usually reliable.


Ca Calcium HCO3 Bicarbonate (Alkalinity)
Mg Magnesium SO4 Sulfate
Na Sodium Cl Chloride
K Potassium No3 Nitrate
Fe Iron (ferrows) F Fluoride


Maintenance Log

  • Record routine maintenance.
  • Record mechanical failures and replacements.
  • Record any change of membrane element locations with element serial numbers.
  • Record replacements or additions of RO devices.
  • Record calibration of all gauges and meters.
  • Record replacement or additions of pretreatment equipment, for example cartridge filters and include date, brand name and nominal rating.
  • Record all cleanings of RO membranes. Include date, duration of cleaning, cleaning agent(s) and concentration, solution pH, temperature during cleaning, flow rate and pressure

Table 1. Factors for estimating TDS from conductivity

Water EC251 (mS/m) K
Permeate 0.1-1 0.50
  30-80 0.55
Seawater 4,500 - 6,000 0.70
Concentrate 6,500-8,500 0.75

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