Water quality
Water quality is a measure of the chemical, physical, and biological characteristics of water, determining its suitability for human consumption, agriculture, industry, and aquatic ecosystems.
- Water quality refers to the chemical, physical, and biological characteristics of water that determine its suitability for supporting life and human use.
- Monitoring these parameters helps identify pollution sources, track ecosystem health, and guide effective management and restoration strategies.
Methods of Assessing Water Quality
Direct (Chemical and Physical) Measurements
1. Dissolved Oxygen (DO)
- Measures how much oxygen is dissolved in water,essential for aquatic life.
- Low DO indicates organic pollution, eutrophication, or thermal pollution.
- Measured using oxygen probes or the Winkler titration method.
- 75% saturation = healthy water
- <10% = severe pollution (e.g., sewage contamination)
A river with turbulent water (like near waterfalls) usually has high DO, while stagnant or polluted areas have low DO.
2. pH
- Indicates the acidity or alkalinity of water.
- Normal freshwater ranges from 6 to 8.
- Deviations suggest acid rain, industrial effluent, or alkaline runoff.
- Measured using pH probes, litmus paper, or pH meters.
- A stream near a coal plant may show pH 4–5 due to acid mine drainage, which releases sulfuric acid into waterways.
- pH < 5.5 can cause fish eggs to fail and mobilize aluminum, which is toxic to gills.
3. Temperature
- Affects dissolved oxygen, metabolic rates, and species distribution.
- Thermal pollution from power plants or industries can reduce oxygen solubility.
- Measured using a digital thermometer or a temperature probe.
When the temperature rises, oxygen solubility falls.
4. Turbidity
Turbidity
Turbidity measures water transparency based on suspended particles (sediments, plankton, pollutants).
- Measures the clarity of water, affected by sediments, organic matter, and algae.
- High turbidity reduces sunlight penetration and affects photosynthesis.
- Measured using a Secchi disc (depth visibility test) or a turbidity tube.
A Secchi disk visibility of less than 0.5 m indicates heavy sedimentation or algal bloom.
ExampleAfter heavy rainfall, river turbidity rises due to runoff and soil erosion, impacting aquatic plants.
5. Nutrient Concentrations (Nitrates and Phosphates)
- High concentrations indicate agricultural runoff or sewage discharge.
- Promote eutrophication, leading to algal blooms and oxygen depletion.
- Measured using colorimetric test kits or test strips.
Typical Ranges:
- Nitrate <5 mg/dm³ = clean
- Nitrate >15 mg/dm³ = polluted
- Phosphate <5 mg/dm³ = clean
- Phosphate >15 mg/dm³ = polluted
The Baltic Sea suffers recurrent algal blooms due to excessive nutrient discharge from nearby farmland.
6. Ammonia
- Indicates sewage pollution or organic decomposition.
- Levels above 1 mg/dm³ are toxic to fish.
- Measured using test kits with color-change reagents.
7. Heavy Metals and Salinity
- Metals such as lead, mercury, and arsenic enter from industrial discharge or mining.
- Salinity changes may indicate seawater intrusion or evaporation in closed systems.
