Water Classification, Safety, and Quality Assessment
1. Classification of Water by Use and Origin
Hygienic Perspective
Origin:
- Rain (atmospheric) water
- Surface water (running, flowing, stagnant)
- Ocean water
- Underground water – formed from atmospheric or surface water
Rain Water:
- Source of all freshwater in the world
- May be collected directly from roofs and other prepared collection systems and stored in cisterns for later use
- Quality is reasonable but it may be contaminated by gases and particles (e.g., SO2 or NO2) that are washed out of the atmosphere or by accumulation of dust and other pollutants.
Surface Water:
- Earliest source of water
- Main source of water-borne epidemics (mainly in the 19th century)
- The development of filtration processes and disinfection of water by chlorination (20th century) made these types of water suitable for community water supply.
Ocean and Brackish Waters:
- Unsuitable for most communities’ water supplies (used only in extreme conditions of necessity)
- Requires desalination
Ground Water:
- Formed by the escape of rainwater through the ground where it is exposed to mineral solutions and then is withdrawn by means of natural springs, wells, etc.
- Tends to be more highly mineralized than surface water
- Higher sanitary quality:
- They are not as likely to be subject to microbial pollution as surface water sources.
- Passage of water through the soil often serves to improve their bacteriological quality.
- Origin: fissures, infiltration of the soil
- Levels: free level (phreatic) or tense level (artesian – water under pressure)
Uses:
- Drinking water (includes bottled and mineral water)
- Bottled water: Origin: underground water
- People chose bottled water for several reasons:
- Preferable taste when compared with tap water
- Transportability
- Appropriate for preparing formula for infants and young children
- Mineral Water:
- Exclusively of underground origin
- Contains 1–3 g of mineral substances per liter
- It may be used for therapeutic purposes (spas, etc.)
- Personal activities (e.g., cooking, bathing, laundering)
- Service water (heating, urban irrigation and street cleaning, fire protection)
- Water for recreational purposes (swimming pools, water parks, hot tubs, spas, public fountains, etc.)
- Process water
- Agricultural purposes (e.g., irrigation, aquaculture)
- Wastewater (e.g., sewage)
Drinking Consumption (per capita) in Developed Countries
Activity | Liters (L) |
---|---|
Drinking and cooking | 3–6 |
Personal hygiene | 10–15 |
Baths and showers | 50–100 |
Laundering | 20–40 |
Dishwashing | 4–10 |
Toilet flushing | 10–15 |
Cleaning apartments | 5–10 |
Car washing | 100 |
Total (average) | 250 |
Lost in pipes | 100–150 |
Drinking Water Safety
Sources:
- 2–10%: local underground systems (e.g., wells) dug or drilled; rather cheap
- Requires regular quality control, disinfection
- >90%: community systems (pipes)
- Partially underground water, partially surface water after processing in treatment plants
Drinking-water safety is secured by the application of a WSP = Water Safety Plan. This plan ensures the safety of drinking water through a comprehensive risk assessment and risk management approach. It encompasses all steps in water supply from catchment to consumer.
- These plans are considered by the WHO as the most effective means of maintaining a safe supply of drinking water to the public.
- It includes operational monitoring of the efficiency of control measures and a final verification of quality.
Water Safety Plan – Key Components:
- System assessment: Determines if the entire drinking water supply chain can supply water of sufficiently high quality to meet regulatory targets.
- Operational monitoring: Identifies control measures to manage risks in the drinking water system. It also defines acceptable water limits and monitoring procedures.
- Management plans: Describe actions for normal and incident conditions. This includes documentation of the water safety plan and communication procedures with other parties involved in drinking water delivery, including consumers.
2. Assessment of Drinking Water
Microbial Water Quality:
- Verification of microbial quality may be undertaken by the supplier, surveillance agencies, or both.
- Involves analysis of fecal indicator microorganisms and may include assessment of specific pathogen densities.
- Organism of choice: Escherichia coli (E. coli) → should not be present in drinking-water.
- While E. coli is a useful indicator, its absence doesn’t guarantee the eradication of more resistant enteric viruses and protozoa.
- Other pathogens used for detection: thermotolerant coliform bacteria (as bacteriophages or bacterial spores)
Chemical Water Quality:
- Relies on comparing water quality analysis results with guideline values.
- Guideline values represent the constituent concentration that doesn’t exceed tolerable health risks over a lifetime of consumption.
- Most chemicals are of concern only with long-term exposure.
- Guidelines include numerous potential hazardous constituents, but few are of public health concern under any circumstance.
- Exceeding a guideline value doesn’t necessarily mean a significant health risk.
- However, exceedance should trigger:
- Investigation into the cause and remedial action.
- Consultation with public health authorities.
Criteria of Health Safety for Tap Water:
- Ensure an adequate supply of microbially safe water and maintain acceptability to discourage consumers from using potentially less safe sources.
- Manage key chemical hazards known to cause adverse health effects.
- Maintain acceptable drinking-water taste, odor, and appearance.
- Apply appropriate technologies to reduce contaminant concentrations in the source below guideline values.