Water Quality Index: Guide to 9 Key Water Parameters
The Water Quality Index is used to evaluate water conditions based on the characteristics of an area and how the water will be used. Several key parameters are commonly regulated by environmental standards. Here is a simplified explanation of each one.
1. pH (Acidity Level)
pH indicates how acidic or alkaline the water is. Typically, water has a pH between 6.5 and 8.5. However, in regions severely affected by acid rain, pH levels can drop to 4.0 or lower.
2. Biochemical Oxygen Demand (BOD)
BOD is one of the most common indicators of water pollution. It shows how much oxygen is required to break down organic pollutants. It is widely used to measure pollution in urban rivers and in wastewater.
After secondary treatment, discharged water must have a BOD of 20 mg/l or less.
3. Chemical Oxygen Demand (COD)
COD is often confused with BOD, but it has a slightly different meaning. It is especially used in water bodies such as lakes, where aquatic plants supply oxygen through photosynthesis. Because of this, the relationship between pollutants and oxygen demand differs from BOD. COD is also measured in mg/l.
4. Suspended Solids (SS)
Suspended solids represent the total amount of solid particles floating in the water, whether organic or inorganic.
• When organic content is high, SS values tend to increase along with BOD and COD.
• When inorganic particles dominate, the water simply appears turbid.
Clarity can be improved through sand filtration and sedimentation.
5. Dissolved Oxygen (DO)
DO refers to the amount of oxygen dissolved in the water. Sufficient DO levels are essential for aquatic life.
Values are generally highest near the water surface due to direct contact with air.
However, when DO reaches 0 (anaerobic conditions) at the bottom, pollutants may be released from the sediment. Aeration and agitation can help improve DO levels.
6. Total Phosphorus (TP)
TP is the total amount of phosphorus in the water, including organic forms, dissolved forms, and phosphate ions. When TP exceeds 0.01 mg/l, the water is close to eutrophic conditions.
7. Total Nitrogen (TN)
TN represents the total nitrogen content in all forms organic, dissolved, and ammonium nitrogen. If TN exceeds 0.1 mg/l, the water is also nearing eutrophication.
8. Chlorophyll-a
Chlorophyll-a measures the amount of chlorophyll in phytoplankton. It indicates the quantity of phytoplankton and their activity level in photosynthesis.
9. Total Organic Carbon (TOC)
TOC measures the amount of organic matter in the water. These substances may be toxic, consume oxygen, or cause odors. Compared to BOD and COD, TOC measurements are faster and easier, making them a practical indicator of pollution.
Conclusion
Understanding the Water Quality Index is essential for evaluating the condition of water in different environments. Each of the nine parameters—pH, BOD, COD, SS, DO, TP, TN, Chlorophyll-a, and TOC, plays a specific role in indicating pollution levels, oxygen availability, nutrient load, and overall ecological health. When analyzed together, these parameters provide a clear picture of water quality and help determine whether the water is suitable for ecosystems, daily use, or wastewater discharge.
By monitoring these indicators, both industries and environmental managers can take the necessary steps to maintain, improve, or restore water quality according to environmental standards.
