Urban Water Supply and Sanitation

Urban Water Sources & Quality - The Wellspring Blueprint

• Sources:
  • Surface: Rivers, lakes (require extensive treatment).
  • Ground: Wells (shallow, deep), springs (generally better quality).
  • Rainwater: Limited, needs storage.
• Quality Standards (IS 10500):
  • Physical: Turbidity <1 NTU (desirable), <5 NTU (permissible); Colour, Odour.
  • Chemical:
    • pH: 6.5-8.5 (acceptable range).
    • TDS: <500 mg/L (desirable); <2000 mg/L (permissible).
    • Hardness (as $CaCO_3$): <200 mg/L (desirable); <600 mg/L (permissible).
    • Fluoride: 1.0-1.5 mg/L (optimal). (📌 <0.5C; >1.5DF; >3SF)
    • Nitrates: <45 mg/L (prevents infant methaemoglobinaemia).
    • Lead: <0.01 mg/L; Arsenic: <0.01 mg/L (toxic).
  • Bacteriological: E. coli 0/100mL in piped water.

⭐ High fluoride (>1.5 mg/L) causes dental fluorosis; >3-6 mg/L skeletal fluorosis. Low fluoride (<0.5 mg/L) causes dental caries. Optimal: 1.0-1.5 mg/L.

Large‑Scale Water Treatment - Taming the Torrent

• Sequence: Storage → Aeration → Coagulation → Flocculation → Sedimentation → Filtration → Disinfection.

• Storage: 10-14 days. Reduces turbidity. Natural purification: ↓bacteria by 90% in 5-7 days.
• Aeration: Removes $CO_2$, $H_2S$, Fe, Mn. ↑$O_2$. Improves taste, odor.
• Coagulation: Alum (Aluminium Sulphate) 5-30 mg/L. Neutralizes charge, forms $Al(OH)_3$ precipitate.
• Flocculation: Gentle, slow mixing. Promotes larger, settleable floc growth.
• Sedimentation: 2-6 hours detention. Gravity settling of flocs. Removes ~90% suspended solids.
• Filtration:
  • Rapid Sand Filter (RSF): Rate 5000-6000 L/hr/m². Mechanical straining. Cleaned by backwashing.
  • Slow Sand Filter (SSF): Rate 100-200 L/hr/m². Biological action via Schmutzdecke (vital layer).

    ⭐ SSF removes 99.9% bacteria; also effective against cysts & ova.

• Disinfection: Chlorination to kill/inactivate pathogens. Aim for free residual chlorine 0.5 mg/L for 1 hr contact.
  • Tests: Orthotolidine (OT), Orthotolidine-arsenite (OTA).

Domestic Water Purification - Safe Sips at Home

• Boiling: Rolling boil for 1-3 minutes. Kills most pathogens. Most effective.
• Chemical Disinfection:
  • Chlorine: 1 drop of 4-6% bleach per liter. Contact time: 30 mins. (📌 Bleach Before Bath)
  • Iodine: 2 drops of 2% tincture per liter. Contact time: 30 mins. Not for pregnant women or thyroid issues.
  • Potassium Permanganate ($KMnO_4$): Pink discoloration. Less effective.
• Filtration:
  • Ceramic filters, slow sand filters (household).
  • Removes suspended impurities, some bacteria/parasites.
• Solar Disinfection (SODIS): PET bottles, 6 hours sun exposure.

⭐ Boiling water for 1 minute kills all common enteric pathogens, including cysts and ova, making it the most reliable household water purification method where feasible.

Urban Sanitation & Waste - Flushing Forward

• Excreta Disposal: Prevents fecal-oral diseases.
  • Unsewered: Sanitary latrines (e.g., PRAI-type); Septic tanks (min. 15m from water source, safe effluent disposal).
  • Sewered: Water carriage system, sewage treatment.
• Solid Waste Management (SWM):
  • Methods: Sanitary landfill (commonest), incineration (hospital waste), composting.
  • Key: Segregation at source.
• Biomedical Waste (BMW) Management: Per BMW Rules, 2016. Strict color-coding & disposal.
• Swachh Bharat Mission - Urban (SBM-U): Aims for ODF towns, 100% scientific SWM.

⭐ Sulabh Shauchalaya: low-cost, twin-pit, pour-flush latrine, widely adopted in India for safe sanitation.

High‑Yield Points - ⚡ Biggest Takeaways

• Piped water supply is ideal for urban areas, aiming for 100% coverage.
• Minimum urban water supply: 135-150 lpcd with full flushing systems.
• Residual chlorine at consumer end: minimum 0.2 mg/L for safety.
• Key waterborne diseases: cholera, typhoid, dysentery, hepatitis A & E.
• Urban sanitation aims for 100% toilet coverage and ODF status.
• Sewage Treatment Plants (STPs) are vital for urban wastewater.
• Integrated solid waste management is crucial for urban environmental health.