The National Water Quality Standards (NWQS) for Malaysia use a range of physical, chemical, and biological parameters to assess water quality. The water quality standards mainly set by the Department of Environment (DOE) are governed by a set of regulations designed to ensure the protection of public health, the environment, and the sustainable use of water resources.
(Reference: https://www.doe.gov.my/en/national-river-water-quality-standards-and-river-water-quality-index/)
Ammoniacal Nitrogen (NH₃-N) is the combined amount of ammonia (NH₃) and ammonium ions (NH₄⁺) in water. It’s a key indicator of water quality, especially in wastewater treatment, environmental monitoring, and aquarium management.
Biochemical Oxygen Demand (BOD) represents the amount of oxygen consumed by bacteria and other microorganisms while they decompose organic matter under aerobic (oxygen is present) conditions at a specified temperature.
Chemical Oxygen Demand (COD) measures the amount of oxygen required to chemically oxidize the organic material and inorganic nutrients, such as Ammonia or Nitrate, present in water.
Dissolved oxygen (DO) refers to the total amount of oxygen currently present in the water. DO originates from the atmosphere or as a byproduct of photosynthesis.
pH is a measure of the concentration of hydrogen ions, the acidity or alkalinity of a solution. The pH-scale is normally between 0 and 14.
Color measures the presence of dissolved organic materials that may cause water discoloration.
Electrical Conductivity is a vital parameter when determining water quality. As salinity and temperature increase, conductivity also increases. The higher the conductivity, the higher number of impurities (dissolved substances, chemicals, and minerals) are in the water.
Floatables are defined as no visible floatable materials or debris in the water.
Odour is due to the presence of substances that have an appreciable vapour pressure and that stimulate the human sensory organs in the nasal and sinus cavities.
Salinity is the measure of the amount of dissolved salts in water.
Taste may be an indication of the presence of potentially harmful substances and some form of pollution or malfunction during water treatment or distribution process.
Total dissolved solids (TDS) is smaller than two microns. It comprises of inorganic salt and small amount of organic matters that dissolve in water, such as soluble hydrogen carbonate ions, chloride salts, sulphates, calcium, magnesium, sodium, potassium, volatile solids and non-volatile solids.
Total suspended solids (TSS) is the concentration of particles suspended in the water column that are larger than two microns in size, such as sand, sediment, algae, bacteria, clay, and silt.
Temperature affects the solubility of oxygen in water and the rate of biological processes.
Turbidity is the measure of relative clarity of the water. It is considered as the simplest and basic indicator of the amount of suspended sediment in the water. It is indicated by how much light is scattered by particles in water.
Fecal coliforms are the group of the total coliforms that are considered to be present specifically in the gut and feces of warm-blooded animals.
Total coliforms include bacteria that are found in the soil, in water that has been influenced by surface water, and in human or animal waste.
The DOE monitors the quality of natural water bodies using a network of monitoring stations across the country. Regulatory frameworks and these water quality data helps inform policy and management decisions related to conservation, pollution control, and ecosystem health, ensuring that the standards are met and enforced, contributing to the sustainable management of water resources.
Water Classes and Uses
| Class | Uses |
| Class I | Conservation of natural environment. |
| Class IIA | Water Supply II – Conventional treatment required. |
| Class IIB | Recreational use with body contact. |
| Class III | Water Supply III – Extensive treatment required. |
| Class IV | Irrigation |
| Class V | None of the above |
