| Coagulation and Sedimentation | Coagulants destabilize particles so they form larger flocs that settle by gravity. | High removal when optimized | Partial removal | Limited removal | No significant removal | Some natural organic matter removal | Can remove particle-bound metals and phosphorus | Low | Handles variable raw-water turbidity; suitable for large flow rates. | Requires chemical dosing, sludge handling, and skilled process control. | Municipal drinking-water pretreatment and surface-water clarification. |
| Media Filtration | Water passes through layers of sand, anthracite, gravel, or other granular media. | High removal after clarification | Partial removal | Limited removal | No significant removal | Limited unless special media are used | Limited dissolved-contaminant removal | Low | Simple, durable, and economical for particle reduction. | Backwashing is required; performance declines if the filter is overloaded. | Drinking-water polishing, process-water pretreatment, and irrigation water. |
| Activated Carbon Adsorption | Dissolved contaminants attach to the large internal surface area of activated carbon. | Moderate particle removal with suitable beds | Not a dependable disinfection barrier | Not a dependable virus barrier | Does not remove most inorganic salts | Effective for many tastes, odors, chlorine, and hydrophobic organics | Can reduce some mercury and other adsorbable compounds | Low to medium | Improves taste and odor; useful for many trace organic compounds. | Media eventually saturates and may require replacement or thermal reactivation. | Drinking-water polishing and removal of taste, odor, and selected organics. |
| Ultrafiltration (UF) | Pressure-driven membranes with very small pores retain particles, colloids, and microorganisms. | Very high removal | High removal of bacteria and protozoa | Variable; depends on membrane integrity and virus size | Little removal of dissolved salts | Limited removal of dissolved organics | Little removal of dissolved metals or nutrients | Low to medium | Produces consistent low-turbidity water and has a compact footprint. | Needs pretreatment and periodic cleaning; does not desalinate water. | Drinking-water clarification, wastewater reuse, and RO pretreatment. |
| Nanofiltration (NF) | A tighter membrane process that removes many multivalent ions and organic molecules. | Very high removal | High removal with intact membranes | High removal with intact membranes | Good reduction of hardness and sulfate; partial desalination | Effective for many larger organic molecules | Effective for hardness, sulfate, and selected metals | Medium | Lower pressure than RO for many applications; reduces hardness and color. | Does not remove all monovalent salts; produces a concentrate stream. | Softening, color removal, industrial process water, and selected reuse systems. |
| Reverse Osmosis (RO) | High-pressure membranes reject dissolved ions, microorganisms, and many dissolved contaminants. | Very high removal after pretreatment | High removal with intact membranes | High removal with intact membranes | High removal of TDS and many inorganic ions | Good for many organics; performance varies by compound | High removal of many metals, nitrate, and other ions | Medium to high; higher for seawater | Broad contaminant reduction and reliable production of low-TDS water. | Higher pressure, membrane fouling, concentrate disposal, and possible remineralization needs. | Desalination, boiler feedwater, drinking water, and high-purity industrial water. |
| Ultraviolet (UV) Disinfection | UV light damages the genetic material of microorganisms and prevents replication. | No physical removal | Effective when dose and UV transmittance are adequate | Effective against many viruses at validated doses | No removal | No significant removal | No removal | Low | No chemical residual, rapid treatment, and no significant change in water chemistry. | Requires low turbidity and reliable electrical power; provides no residual protection. | Final disinfection for drinking water, wastewater reuse, and process water. |
| Ozonation | Ozone oxidizes microorganisms, taste-and-odor compounds, and selected organic contaminants. | Limited particle removal | Strong disinfection capability | Effective at validated doses | No significant salt removal | Oxidizes many taste, odor, and color compounds | Can oxidize iron and manganese for subsequent filtration | Medium | Powerful oxidant and disinfectant; improves taste, odor, and color. | Must be generated on site; ozone off-gas control and bromate management may be required. | Surface-water treatment, advanced oxidation, and high-quality reuse applications. |
| Ion Exchange | Resins exchange undesirable ions in water for safer or less problematic ions. | No significant particle removal | No disinfection | No disinfection | Selective removal; not a universal desalination process | Generally ineffective for most organics | Effective for selected ions such as hardness, nitrate, and some metals | Low | Selective and efficient for targeted ionic contaminants. | Resin exhaustion, regeneration chemicals, and brine or spent-resin management are required. | Water softening, nitrate reduction, demineralization, and industrial polishing. |
| Electrocoagulation | Electric current releases coagulant species from sacrificial electrodes to destabilize contaminants. | High for many suspended solids and emulsions | Partial reduction | Not normally a stand-alone virus barrier | Limited dissolved-salt removal | Can reduce oils, emulsions, and selected organics | Can remove certain metals and phosphorus | Medium | Can reduce chemical coagulant handling and treat difficult industrial wastewaters. | Electrode consumption, electrical control, sludge production, and scale formation may occur. | Industrial wastewater, oily water, and difficult-to-coagulate streams. |