Water: Sources, Diseases and Quality

The basic physiological requirement of drinking water is 2L/day. Daily supply per capita is adequate to meet the needs of all urban domestic purposes. The main Sources of Water:

• Rain- Rainwater is the purest form of water. Rainwater is very soft with traces of 0.0005% solids.
• Surface water
  • Impounding reservoirs
  • Rivers and streams
  • Ponds and lakes
• Groundwater is the Cheapest and most practical means of providing water to small communities. It is superior to surface water as it provides an effective filtering medium, and there is less chance of contamination in groundwater.
  • Advantages of groundwater:
    • Free from pathogenic organisms
    • Requires no treatment.
    • Supply is sufficient during dry seasons.
    • Less subject to contamination than surface water
  • Disadvantages of groundwater:
    • High mineral content. Examples: salts and calcium, magnesium which makes water hard.
    • Pumping is required to lift.
  • The main sources of groundwater are:
    • Shallow well- Shallow wells are most commonly used in India
    • Deep well- Deep wells provide the safest water and are the most satisfactory source of water supply. Artesian wells are a type of deep well in which water rises above the level of groundwater as it is held under pressure between 2 impervious strata. Artesian wells are not common in India.
    • Springs

It becomes very important to know about the Disinfection of Wells as it is a widely used source of water in india. This requires a mass scale of disinfection during epidemics like cholera and gastroenteritis. The Most effective and cheap method of disinfecting a well is using bleaching powder. 2.5g of good-quality bleaching powder would be required to disinfect 100 L of water. We can get the estimate of the quantity of bleaching powder required using the Horrocks apparatus. The Formula used to calculate the amount is 3.12 x d2 x h (d= diameter h= height).

The main Criteria for identifying Problem Habitats are that the Drinking water source point is not within 1.6 km in plains or 100m in hill areas. Water must be available at a depth of >15m. At Least one hand pump (safe water spot) should be present for a population of 250 people.

It is very important to learn about the Public Health Classification of Water and Diseases. They are divided into:

• Waterborne diseases: The diseases that are contracted by Drinking contaminated water
  • Diarrhea
  • Typhoid
  • Cholera
  • Hepatitis A and E
  • Gastrointestinal infections
  • Polio
• Water Washed Diseases or Water Scarcity Diseases: These include the diseases that are caused by Inadequate amounts of water to maintain personal hygiene.
  • Infective trachoma
  • Conjunctivitis
  • Scabies
  • Bacillary Amoebic dysentery
  • Worm infestations
• Water-Based Disease: These diseases occur due  to intermediate host present in water
  • Schistosomiasis (snails)
  • Cyclopes: Guinea worm disease/ dracunculiasis)
• Water Related/ Breeding Diseases: Vectors of certain diseases require water for breeding (mosquito-borne)
  • Anopheles (malaria) needs clean water.
  • Culex needs dirty water for Japanese encephalitis.
  • Aedes, dengue, and chikungunya in artificial water collection sources.

Water is one of the sources of life. We just read how different contaminations can result in some life threatening diseases. The Water Quality of the Source of water has certain criteria and Standards that need to be followed before the water is fit to use. Water quality can be assessed on the following criteria(guidelines):

• Acceptability aspects: it includes the physical and chemical properties of water. Physical Properties are:
  • Turbidity: Up to 5 NTU (Nephelometric turbidity unit)
  • Color: Up to 15 TCU (true color unit) or 5 Hazen unit
  • Taste and odor: Tasteless, odorless

The chemical properties that decide if the water is usable or not are:

• Chlorides: The standard which is prescribed for chloride is 200 mg/L maximum prescribed level is 600mg/L. Excess NaCl causes CVDs (cardiovascular diseases)
• Hardness: Recommended between 100-300 mg/L is acceptable. Softening of water is recommended at 150 mg/L
• pH: 6.5-8.5: Chlorine acts best at pH 7.
• Hydrogen sulfide: Taste and odor threshold should be at 0.05-0.1 mg/L
• Iron: A reddish brown color occurs when ferrous iron in groundwater oxidizes to ferric iron. Iron level is up to 0.3 mg/L
• Total dissolved solids: <600 mg/L is good. Prescribed permissible level TDS can go up to 1000 mg/L
• Microbiological aspects:
  • Most reliable evidence for fecal contamination-Coliform bacteria.
  • Evidence for recent contamination - Fecal streptococci
  • Remote contamination - Clostridium perfringens
  • Two ways are used as the Screening test for the presence of E. coli
    • Multiple tube method- 72-96 hours for the result
    • Membrane filtration Technique- 20 hours for the result.
  • Confirmatory test for E coli are:
    • Eijkman test,
    • Indole production
    • Citrate utilization
• Chemical aspects:
  • The Most undesirable metal in water is lead
  • Nitrate is a Remote contamination indicator, While Nitrite is a Recent contamination indicator. If both are present, the amount should be <= 1 mg/L
• Radiological aspects: Proposed guideline values for radioactivity in drinking water
  • Gross alpha activity 0.5 Bq/L 
  • Gross beta activity 0.1 Bq/L

A topic that can be asked in competitive exams like NEET-PG, NEXT, and FMGE examination is the Hardness of Water. The hardness of water is defined as soap destroying the power of Water. Temporary hardness is because of Ca and Mg salts of bicarbonates. The hardness of water is expressed in terms of Milliequivalents per liter (meq/L) of CaCO3

1 meq/L hardness = 50 mg CaCO3 (50 ppm) per liter of water.

• Soft water: <1 (<50 mg/l)
• Moderately Hard water: 1-2 (50-150 mg/l)
• Hard water:3-6 (150-300 mg/l)
• Very hard water: >6 (>300 mg/l)

Before we finish this blog, the Key Guideline Aspects of WHO Recommended Drinking Water Quality are Summarized below:

• Turbidity: 5 NTU
• Color: 15 TCU
• Chloride: 600 mg/L
• TDS: 1000 mg/L
• Hardness: 100-300 mg/L
• Coliform: 0 coliform per 100 mL of water
• Lead: 0.01 mg/L
• Fluoride: 0.5-0.8 mg/L
• Nitrate: < 50 mg/L
• Nitrite: <3 mg/L

Also Read: Asha: Accessibility, Functions, Obligations, Compensation, Benefits And Facilitators of Asha

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