Comprehensive Study Notes – Water Quality, Standards & Treatment

Introduction to Water Quality

• Water supply systems demand water that meets specific physical, chemical, biological and other quality criteria.
• Conventional treatment steps: screening → grit removal → aeration → coagulation → flocculation → sedimentation → filtration → fluoridation → disinfection → conditioning.
• Certain contaminants (e.g.
  • $\text{Na}$, $\text{Mg}$, \text{NO3^-}, \text{SO4^{2-}}, heavy metals) cannot be fully removed by conventional methods and require special/advanced treatment such as algae control, pre-chlorination, ozonation, activated-carbon adsorption or specialised sludge handling.

Recommended Raw-Water Quality & Monitoring

• Parameters divided into Groups I–V (microbial, general physical–chemical, toxic metals, pesticides & herbicides, radioactivity).
• Monitoring frequency codes
  • $W$ = weekly $M$ = monthly $Y/4$ = once every 3 months $Y$ = annual $WN$ = when necessary.
• Illustrative limits (surface / ground / direct impounding)
  • Total coliform: $5{,}000\;\text{MPN\,or\,CFU}/100\text{ mL}$ (Group I – microbial).
  • Turbidity: $1{,}000\;\text{NTU}$ (raw water upper limit).
  • Colour: $300\;\text{TCU}$.
  • pH range: $5.5{-}9.0$.
  • Dissolved solids: $1{,}500\;\text{mg/L}$.
  • Key toxic elements (Group III) & limits: $\text{Hg}=0.001$, $\text{Cd}=0.003$, $\text{Se}=0.01$, $\text{As}=0.01$, $\text{Pb}=0.05$ ($\text{mg/L}$).
  • 40 parameters in raw-water list, 131 in treated-water list.
• Samples must be taken more frequently if source is known/suspected to exceed limits.

Drinking-Water Quality Standards (Plant Outlet → Reservoir → Distribution)

• Microbiological
  • Total coliform & $E.\,coli$: “not detected” in any $100\text{ mL}$ sample.
  • Faecal streptococci, clostridia, viruses, protozoa, helminths: absent in $100\text{ mL}$.
• Physical
  • Turbidity $\le 5\;\text{NTU}$.
  • Colour $\le 15\;\text{TCU}$.
  • pH $6.5{-}9.0$.
  • Free residual chlorine $0.2{-}5.0\;\text{mg/L}$; combined residual $\ge 1.0\;\text{mg/L}$.
• Inorganic chemicals (examples of maximum acceptable values)
  • Total dissolved solids $\le 1{,}000\;\text{mg/L}$.
  • Chloride $\le 250\;\text{mg/L}$.
  • Ammonia $\le 1.5\;\text{mg/L\,(as\,N)}$.
  • Nitrate $\le 10\;\text{mg/L\,(as\,N)}$.
  • Iron $\le 0.3\;\text{mg/L}$; Manganese $\le 0.1\;\text{mg/L}$.
  • Hardness: design target $100\;\text{mg/L}$, absolute $\le 500\;\text{mg/L}$.
  • Aluminium $\le 0.2\;\text{mg/L}$.
• Organic/radiological
  • Trihalomethanes (THMs): sum of ratios $\le 1$; key individual limits – chloroform $0.2\;\text{mg/L}$, bromoform $0.1\;\text{mg/L}$.
  • Gross $\alpha$: $0.1\;\text{Bq/L}$, Gross $\beta$: $1.0\;\text{Bq/L}$.

Physical Quality Parameters

Colour

• Natural waters are ideally colourless.
• Caused by humic/fulvic compounds; acceptable
  • Raw water $<300\,\text{TCU}$ (conventional treatment handles $<75\,\text{TCU}$).
  • Drinking water $<15\,\text{TCU}$.
• Measured spectrophotometrically (expressed as TCU).

Turbidity

• Results from suspended solids (silt, clay, FDOM).
• Signifies clarity & possible microbial shielding.
  • Raw water permissible peak $1{,}000\,\text{NTU}$.
  • Finished water $\le 5\,\text{NTU}$ (regulatory).
• Measured with nephelometric turbidimeter (NTU units).

Taste & Odour

• Trace organics/inorganics (e.g. algae by-products, hydrogen sulphide, chlorophenols) impair palatability.
• Control options: aeration, chemical pre-treatment (algaecides), pre-chlorination, activated-carbon adsorption.

Suspended Solids & TDS

• Suspended solids – plankton, clay, silt; correlate with turbidity.
• TSS often elevate TDS; TDS $\le 1{,}500\,\text{mg/L}$ (design aim $1{,}000\,\text{mg/L}$ to assure taste, hardness & corrosion control).

Temperature

• Ideal potable water temperature $10{-}15^{\circ}\text{C}$; extremes affect taste and treatment chemistry.
• Source selection should consider seasonal variation.

Chemical Quality Parameters

Inorganic Contaminants (selected)

• Arsenic: limit $0.05\,\text{mg/L}$; sources—pesticides, mining; conventional limit same for raw water.
• Cadmium: $0.005\,\text{mg/L}$; plating, photography; removed at $\text{pH}>8$ via coagulation.
• Chromium (VI): $0.05\,\text{mg/L}$; industrial.
• Cyanide: $0.1\,\text{mg/L}$; mining effluent; chlorine treatment removes $90{-}100\%$.
• Fluoride: problem >$1.5\,\text{mg/L}$; conventional removal ineffective → seek alternate source.
• Lead: $0.05\,\text{mg/L}$; corrosion of plumbing; alum coagulation helpful.
• Mercury: $0.001\,\text{mg/L}$; mostly inorganic in water; removed by activated-carbon.
• Nitrate-N: $10\,\text{mg/L}$ (equiv. 45\,\text{mg/L\,NO_3^-}); high levels cause infant methaemoglobinaemia (blue-baby syndrome). Sources: fertilisers, animal waste.
• Selenium: $0.01\,\text{mg/L}$; copper smelters; toxicity threshold $0.01{-}0.1\,\text{mg kg}^{-1}\text{/day}$ body weight.

Organic Contaminants

• Natural organics: humic/fulvic acids (0–$30\,\text{mg/L}$) → precursors to disinfection by-products.
• PAHs: tar, incomplete combustion; limit $0.0002\,\text{mg/L}$ in treated water.
• Pesticides & herbicides (e.g. aldrin/dieldrin $0.00003\,\text{mg/L}$, atrazine $0.002\,\text{mg/L}$) monitored quarterly or as required.
• Trihalomethanes (THMs): formed when chlorine reacts with organic matter; control by organic precursor removal pre-chlorination.

Microbiological Quality Parameters

• Raw water indicators: total coliform (TC) & faecal coliform (FC).
  • High TC → general sewage contamination; high FC/$E.\,coli$ → human/animal faecal origin.
  • Raw water alert: if $1{-}10$ coliforms/$100\,\text{mL}$ consistently detected, urgent mitigation.
  • Raw water maxima: $TC=5{,}000\,\text{MPN}/100\,\text{mL}$.
• Drinking water standard: $TC=0$ and $E.\,coli=0$ per $100\,\text{mL}$.

Other Important Parameters

• pH: raw waters generally $4{-}9$; treated water recommended $6.5{-}9.0$ (≈$60\%$ of Malaysian rivers between $6.5{-}8.5$).
• Biochemical Oxygen Demand (BOD): indicator of organic pollution.
  • Raw water guideline $<6\,\text{mg/L}$.
  • Classification: $0{-}4$ clear; $4{-}8$ mildly; $8{-}12$ moderately; $>12$ grossly polluted.
• Ammoniacal-N: impacts chlorine demand.
  • Treated water target $<0.5\,\text{mg/L}$.
  • Removal: breakpoint chlorination or biological nitrification.
• Aluminium (residual): $<0.2\,\text{mg/L}$; excess arises from over-dosing alum.
• Chloride: taste/corrosion; drinking limit $250\,\text{mg/L}$ (desalination expensive → prefer low-Cl- sources).
• Hardness: carbonate & non-carbonate; Malaysian rivers mostly $<60\,\text{mg/L}$, design standard $100\,\text{mg/L}$; accept up to $500\,\text{mg/L}$ in raw water.
• Iron: rivers $1{-}5\,\text{mg/L}$; treat if $>0.3\,\text{mg/L}$ (prechlorination, aeration + coagulation).
• Manganese: treated limit $0.1\,\text{mg/L}$; sometimes oxidised by \text{KMnO_4} dosing.

Malaysian Legislation & Classification

• National Water Quality Standards (NWQS, MWA 2021) align with WHO but adapt to local conditions (tropical climate, monsoon run-off).
• DOE Water Quality Index (WQI)
  • Six parameters: DO, BOD, COD, TSS, NH$_3$-N, pH.
  • Water-class linkage:
  • Class I: pristine; drinking after minimal treatment; fishery I (very sensitive species).
  • Class IIA: conventional treatment; fishery II.
  • Class IIB: recreational body-contact.
  • Class III: extensive treatment; fishery III; livestock.
  • Class IV: irrigation; Class V: non-classified.
  • WQI score interpretation
  • $>92.7$ Class I $76.5{-}92.7$ Class II $51.9{-}76.5$ Class III $31{-}51.9$ Class IV $<31$ Class V.
  • Pollution status
  • Clean $81{-}100$, slightly polluted $60{-}80$, polluted $0{-}59$.
• Real-time dashboard (24 Feb 2025): 30 stations – 18 clean, 11 slightly polluted, 1 polluted (Sg. Klang WQI $58$).

Water Supply Issues & Sustainability

• Finite freshwater despite perception of abundance; spatial & temporal scarcity exacerbated by:
  • Rapid urbanisation & population growth.
  • Inadequate/aged infrastructure ⇒ high non-revenue water (NRW).
  • Low consumer tariffs → under-financing O & M.
  • Pollution from industrial, agricultural, domestic sources.
  • Climate change introduces hydrological uncertainty and irreversible ecosystem shifts.

Ethical, Practical & Cross-lecture Connections

• Public-health ethics: ensuring safe, palatable water prevents water-borne disease; failure disproportionately hurts vulnerable communities.
• Economic implications: cost of advanced treatment vs. preventive watershed protection.
• Engineering design: choice of source, process selection (advanced oxidation, membrane filtration) hinges on parameter exceedance highlighted above.
• Policy tie-in: complying with WHO 1993/96 guidelines (chemical updates) and adopting adaptive management under Malaysian Environmental Quality Act.

Key Numerical References (LaTeX format examples)

• $\text{Turbidity}<em>{\text{raw}}\le 1{,}000\;\text{NTU}$ $\text{Turbidity}</em>{\text{drink}}\le 5\;\text{NTU}$
• $\text{Colour}<em>{\text{drink}}<15\;\text{TCU}$ $\text{Colour}</em>{\text{raw}}<300\;\text{TCU}$
• $\text{TDS}_{\text{limit}}=1{,}500\;\text{mg/L}$ (design target $1{,}000\;\text{mg/L}$)
• $\text{pH}_{\text{drink}}=6.5{-}9.0$
• $\text{Nitrate\,(as\,N)}_{\max}=10\;\text{mg/L}$
• $E.\,coli_{\max}=0\;\text{MPN}/100\,\text{mL}$

Study Tips & Real-World Relevance

• Memorise Group I microbial zero-tolerance for treated water – most exam questions target this critical health criterion.
• Understand why some contaminants (e.g. fluoride, sodium, sulphate) pass through conventional plants → know which advanced processes address them (e.g. ion exchange, RO).
• Link WQI classifications to treatment depth: Class IIA → conventional; Class III → ext. treatment; exam scenarios frequently ask to recommend process trains.
• Watch for units: many limits switch between $\text{mg/L\,(as\,N)}$ and \text{mg/L\,(NO_3^-)}.
• Ethical dimension: balancing affordability with stringent standards; rate-setting and NRW reduction feature in policy essays.