| Source water (surface water) | Algae bloom | Increased nutrientsWarm weatherStagnated water |
| A build-up of sediment over intake | Changing watercourseAn issue with intake design |
| Excessive turbidity or colour after rain | Runoff |
| Source water (groundwater) | The bore ‘drawdown’ increasing | Water demand exceeding the capacity of the boreIncreased water extraction from the aquiferLess water entering the aquiferPlugging of bore screenGradual blockage of the area around the bore affecting water recharge
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| E. coli previously absent but now present | Contaminated water entering bore from the surfaceContamination of aquiferChange of land use or waste disposal |
| Change in turbidity or colour | Surface water intrusion into the boreDamaged well screen or casing corrodedDrawing in water from a different part of the aquifer |
| Water turbid during the first stages of pumping | The rising main within the bore is corroding |
| Sand in bore discharge and/or excessive pump impeller wear | Damaged well screen or casing is corrodedFlow drawing sand into the wellRapid stop/start pumping agitating the bore and not flushing out the sand |
| Sudden change in flow rate | A flow restricting valve left openA leaking pipeDamaged 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-treatmentDamaged pre-treatment system |
| Lack of flow | Blockages |
| Pre-treatment (filter) | Rapid increase in head loss and short filter runs | Incoming water is too dirty |
| One filter blocking much earlier than the others | Excessive flows to an individual filter |
| If the flow is decreased or the water becomes dirty or cloudy | The filter needs to be checked and may need replacing. |
| Spikes in filtered water turbidity during a filter run | Sudden 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 turbidity | Changing filters too late |
| High filtered water turbidity | Filter pores too largeFilter starting to unloadRuptured cartridge |
| Heterotrophic plate count increases across the filter | By concentrating particles in one area, cartridge filters can contribute to the growth of non-coliform bacteria. |
| Initial pressure differential is low | Cartridge 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 dirtyInadequate backwashingAir blinding in the filter |
| Visible mud balls or cracking | Backwash unable to remove mud and silt |
| Backwash unable to remove mud and silt | Troughs not levelTroughs in the wrong places |
| Encrustation of media | Build-up of scale or other fouling on media |
| Filter media in troughs | Loss of media with the backwash water |
| Spikes in filtered water turbidity during a filter run | Sudden changes in flow rate to a filter or filtersPoor coagulant dosingGrowths in the underdrains |
| High turbidity at the end of a filter run | Initiating backwashes too late |
| High turbidity at the start of a filter run | Residual turbidity being washed out of media |
| Water storage (tank) | Algae growing in water storage | Stored water containing nutrients is exposed to light |
| Stored raw water of poor quality seasonally – commonly high manganese and sulphide levels | In 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 tankPoor flow path across the tankParticles are too fine to settle out before the water leaves the tank |
| Disinfection (chemical oxidant) | Insufficient disinfectant residual | High disinfectant demand from the waterPoorly operating or inoperative disinfection equipmentDisinfection has run outDosing pump malfunction due to incorrect calibration or faulty pump controllerIncorrectly 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 disinfectionSystem has been contaminatedpH is too highParticles are masking the effect of the chlorineHigh concentrations of biofilms |
| Free available disinfectant declines over time even though the dose rate is the same | Sodium and calcium hypochlorite solution breaks down over time. |
| Disinfection (UV) | UV intensity low | Fouling of lamp sleevesLamps are at the end of their service lifeDecrease in UV transmittance of the water – the minimum acceptable value is usually 80% |
| Lamp not working | Lamp or ballast failure |
| Storage (header tanks) | Wide fluctuations in the residual chlorine concentrations leaving the tank | Poor mixingVariation in water use |
| Deterioration in water quality when water levels low; possible taste and odour issues | Sludge and scum accumulating in the tank |
| Shed | Nipple blocked | ScaleTurbidityParticles getting through the filter |
| Pipe corroding | Acidic waterAged pipes |
| Red water or reddish-brown staining | Corrosion of iron pipes or the presence of iron in the water |
| Bluish stains on fixtures | Corrosion of copper service lines |
| Black water | Sulphide corrosion of iron or copper lines |
| Foul tastes and odours | By-products of microbial activity facilitated by corrosive conditions |
| Loss of pressure | Excessive scaling, tuberculation, pitting and galvanic corrosion |
| Short service life of the plumbing | Rapid deterioration of pipes caused by corrosive conditions |
| Cream scale | Magnesium and calcium scale |
| Red scale | Iron scale |
| Black scale | Manganese scale |
| Red or black scale | Iron and manganese scale |
