Industry best practice manual for water quality management and sterilisation on-farm

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Issue identification and possible causes

Table 27. Troubleshooting common water quality issues and their causes

Water treatment system IssuePossible cause(s)
Source water (surface water)Algae bloom
  • Increased nutrients
  • Warm weather
  • Stagnated water
  • A build-up of sediment over intake
  • Changing watercourse
  • An issue with intake design
  • Excessive turbidity or colour after rainRunoff
    Source water (groundwater)The bore ‘drawdown’ increasing
  • Water demand exceeding the capacity of the bore
  • Increased water extraction from the aquifer
  • Less water entering the aquifer
  • Plugging of bore screen
  • Gradual blockage of the area around the bore affecting water recharge

  • E. coli previously absent but now present
  • Contaminated water entering bore from the surface
  • Contamination of aquifer
  • Change of land use or waste disposal
  • Change in turbidity or colour
  • Surface water intrusion into the bore
  • Damaged well screen or casing corroded
  • Drawing in water from a different part of the aquifer
  • Water turbid during the first stages of pumpingThe rising main within the bore is corroding
    Sand in bore discharge and/or excessive pump impeller wear
  • Damaged well screen or casing is corroded
  • Flow drawing sand into the well
  • Rapid stop/start pumping agitating the bore and not flushing out the sand
  • Sudden change in flow rate
  • A flow restricting valve left open
  • A leaking pipe
  • Damaged pump
  • Pre-treatment (general)No difference in suspended solids between source and filter water samples
  • Suspended solids smaller than the cut-off size for pre-treatment
  • Damaged pre-treatment system
  • Lack of flowBlockages
    Pre-treatment (filter)Rapid increase in head loss and short filter runsIncoming water is too dirty
    One filter blocking much earlier than the othersExcessive flows to an individual filter
    If the flow is decreased or the water becomes dirty or cloudyThe filter needs to be checked and may need replacing.
    Spikes in filtered water turbidity during a filter runSudden changes in flow rate to a filter or filters are causing them to unload, particularly where high-pressure levels are allowed to build up.
    Flow declining and possible increase in treated water turbidityChanging filters too late
    High filtered water turbidity
  • Filter pores too large
  • Filter starting to unload
  • Ruptured cartridge
  • Heterotrophic plate count increases across the filterBy concentrating particles in one area, cartridge filters can contribute to the growth of non-coliform bacteria.
    Initial pressure differential is lowCartridge is not sitting on the seal properly
    Pre-treatment (sand / activated carbon filter)Rapid increase in head loss and short filter runs
  • Incoming water is too dirty
  • Inadequate backwashing
  • Air blinding in the filter
  • Visible mud balls or crackingBackwash unable to remove mud and silt
    Backwash unable to remove mud and silt
  • Troughs not level
  • Troughs in the wrong places
  • Encrustation of mediaBuild-up of scale or other fouling on media
    Filter media in troughsLoss of media with the backwash water
    Spikes in filtered water turbidity during a filter run
  • Sudden changes in flow rate to a filter or filters
  • Poor coagulant dosing
  • Growths in the underdrains
  • High turbidity at the end of a filter runInitiating backwashes too late
    High turbidity at the start of a filter runResidual turbidity being washed out of media
    Water storage (tank)Algae growing in water storageStored water containing nutrients is exposed to light
    Stored raw water of poor quality seasonally – commonly high manganese and sulphide levelsIn large, deep reservoirs, the upper layers can cool enough to cause a circulation current which brings settled material up from the bottom layer.
    Poor solids removal across the tank
  • Sediment build-up in the tank
  • Poor flow path across the tank
  • Particles are too fine to settle out before the water leaves the tank
  • Disinfection (chemical oxidant)Insufficient disinfectant residual
  • High disinfectant demand from the water
  • Poorly operating or inoperative disinfection equipment
  • Disinfection has run out
  • Dosing pump malfunction due to incorrect calibration or faulty pump controller
  • Incorrectly calculated disinfectant dose
  • E. coli detected after disinfection, even though the dose and contact time seem okay
  • Short-circuiting means retention time is insufficient for disinfection
  • System has been contaminated
  • pH is too high
  • Particles are masking the effect of the chlorine
  • High concentrations of biofilms
  • Free available disinfectant declines over time even though the dose rate is the sameSodium and calcium hypochlorite solution breaks down over time.
    Disinfection (UV)UV intensity low
  • Fouling of lamp sleeves
  • Lamps are at the end of their service life
  • Decrease in UV transmittance of the water – the minimum acceptable value is usually 80%
  • Lamp not workingLamp or ballast failure
    Storage (header tanks)Wide fluctuations in the residual chlorine concentrations leaving the tank
  • Poor mixing
  • Variation in water use
  • Deterioration in water quality when water levels low; possible taste and odour issuesSludge and scum accumulating in the tank
    ShedNipple blocked
  • Scale
  • Turbidity
  • Particles getting through the filter
  • Pipe corroding
  • Acidic water
  • Aged pipes
  • Red water or reddish-brown stainingCorrosion of iron pipes or the presence of iron in the water
    Bluish stains on fixturesCorrosion of copper service lines
    Black waterSulphide corrosion of iron or copper lines
    Foul tastes and odoursBy-products of microbial activity facilitated by corrosive conditions
    Loss of pressureExcessive scaling, tuberculation, pitting and galvanic corrosion
    Short service life of the plumbingRapid deterioration of pipes caused by corrosive conditions
    Cream scaleMagnesium and calcium scale
    Red scaleIron scale
    Black scaleManganese scale
    Red or black scaleIron and manganese scale
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