Drinking water pollutants include physical (sediments, turbidity), chemical (heavy metals, pesticides, nitrates), biological (bacteria, viruses, protozoa), and radiological contaminants. Treatment methods involve conventional steps like coagulation, filtration, and disinfection, alongside modern technologies such as membrane filtration, advanced oxidation, and UV or ozone treatment to ensure safe, healthy water.

Drinking water can contain a wide spectrum of pollutants, originating from natural sources, industrial discharges, agricultural activities, and distribution systems. These contaminants can be broadly classified as follows:

1. Major Pollutants in Drinking Water

A. Physical Pollutants

• Turbidity (suspended solids, clay, silt, organic matter)
• Color (humic substances, metals like iron and manganese)
• Taste and odor compounds (e.g., geosmin, algal metabolites)

B. Chemical Pollutants

· Heavy metals: lead (Pb), mercury (Hg), cadmium (Cd), arsenic (As), chromium (Cr), copper (Cu)

· Nitrate (NO₃⁻), nitrite (NO₂⁻), fluoride (F⁻), cyanide

· Salinity (chlorides, sulfates, hardness ions like Ca²⁺, Mg²⁺)

· Pesticides and herbicides (atrazine, glyphosate, DDT residues)

· Industrial solvents (benzene, toluene, trichloroethylene)

· Petroleum hydrocarbons and phenols

· Disinfection by-products (trihalomethanes, haloacetic acids)

· Radon, uranium, radium, cesium, strontium

C. Biological Pollutants

• Bacteria: Escherichia coli, Salmonella, Vibrio cholerae
• Viruses: enteroviruses, hepatitis A virus, rotavirus
• Protozoa: Giardia lamblia, Cryptosporidium parvum
• Helminths (in endemic regions)

2. Treatment Methods

Treatment depends on the nature of pollutants; modern water treatment generally combines multi-barrier approaches:

A. For Physical Pollutants

• Screening & Sedimentation: removal of large debris and suspended solids
• Coagulation–Flocculation: addition of alum, ferric salts, or polymers to destabilize and aggregate fine particles
• Filtration: sand filters, rapid gravity filters, membrane filtration (microfiltration, ultrafiltration)

B. For Chemical Pollutants

· Ion exchange (for nitrates, hardness, heavy metals)

· Reverse osmosis or nanofiltration (for salts, fluoride, arsenic)

· Precipitation methods (lime softening for hardness, coagulation for heavy metals)

· Adsorption (activated alumina for fluoride, iron-based adsorbents for arsenic)

· Activated carbon adsorption (pesticides, solvents, taste and odor compounds)

· Advanced Oxidation Processes (ozonation, UV/H₂O₂, photocatalysis) for persistent organic pollutants

· Air stripping (for volatile organic compounds, VOCs)

· Ion exchange resins

· Reverse osmosis

· Precipitation and co-precipitation

C. For Biological Pollutants

In practice, conventional water treatment plants combine:

Precisely speaking drinking water can pick up many kinds of pollution from germs like bacteria, viruses, and parasites, to dirt and turbidity, to harmful chemicals such as arsenic, lead, nitrates, pesticides, and even traces of medicines or radioactive elements. To make it safe, different treatments are used: filtering and settling remove particles, disinfectants like chlorine, ozone, or UV light kill microbes, and advanced methods like activated carbon, ion exchange, or reverse osmosis tackle chemicals. Big treatment plants usually combine several steps, while households may rely on simpler solutions like boiling, solar disinfection, or ceramic filters to keep water clean and healthy.

Drinking water pollution refers to the presence of harmful substances (contaminants) in water sources like rivers, lakes, and groundwater, making it unsafe for human consumption. These pollutants can originate from a variety of natural and human-made sources.

Water pollutants can be categorized into several types:

1. Biological Pollutants (Pathogens)

These are microorganisms that cause waterborne diseases. Example Bacteria: (E. coli, Vibrio cholerae (cholera), Salmonella typhi (typhoid), Legionella (Legionnaires' disease)), Viruses: (Hepatitis A, Norovirus, Rotavirus), Protozoa:(Giardia lamblia, Chryptosporidium parvum, Parasitic Worms: Like those causing schistosomiasis.

2. Chemical Pollutants including both inorganic and organic compounds.

A. Inorganic Chemicals like Heavy Metals, Lead from old lead pipes and solder which causes neurological damage, especially in children, Mercury from industrial discharges and mining, Arsenic, Cadmium, Nutrients, Nitrates & Phosphates, primarily from agricultural fertilizer runoff and sewage. They cause algal blooms (eutrophication), which deplete oxygen and can produce toxins.

Other Inorganics include Fluoride and Cyanide.

B. Organic Chemicals includes Pesticides & Herbicides, Volatile Organic Compounds (VOCs) (Such as benzene (from petroleum), trichloroethylene (from industrial solvents)), Disinfection Byproducts (DBPs) formed when disinfectants (like chlorine) react with natural organic matter in water. Examples are trihalomethanes (THMs) and haloacetic acids (HAAs), which are linked to cancer risks, Pharmaceuticals and Personal Care Products (PPCPs) like Residues from medications, hormones, cosmetics, and detergents that pass through wastewater treatment plants. Per- and Polyfluoroalkyl Substances (PFAS) Known as "forever chemicals" used in non-stick cookware, firefighting foam, etc.

3. Physical Pollutants like Sediment/Suspended Solids,Temperature, etc.

4. Radiological Pollutants like Radionuclides such as radium, uranium, and radon gas.

Methods for Water Treatment

Water treatment involves a multi-step process, often called a "treatment train," designed to remove different types of contaminants sequentially. A typical municipal water treatment plant uses the following methods:

1. Preliminary Treatment (Screening) which removes large debris like sticks, leaves, and plastic and Grit like Sand, gravel, and other heavy particles.

2. Primary Treatment (Coagulation, Flocculation, Sedimentation) which targets suspended solids and colloidal particles.

Coagulation: Chemicals like alum (aluminum sulfate) or ferric chloride are added. They neutralize the negative charges on fine particles, allowing them to clump together.

Flocculation: The water is gently mixed, causing the coagulated particles to form larger, heavier clumps called "flocs."

Sedimentation: The water flows into a quiet settlement tank where the heavy flocs settle to the bottom by gravity and are removed as sludge.

3. Secondary Treatment (Filtration) which removes the remaining smaller particles, including some microbes and organic matter.

4. Disinfection (Tertiary Treatment) which is the critical final step to kill any remaining pathogens.

Water is polluted in three ways: physical pollutants, including dust from humans or from nature, such as floods and dust storms, as well as solid materials from plants and industrial materials such as plastic bottles and others. The second type is chemical pollutants, which are the most dangerous and result from the decomposition of materials and their transformation into other substances, such as salinity, pH, and many other substances. The third type is biological pollutants resulting from the growth of harmful bacteria and fungi.