The goal of water treatment is to reduce or remove all contaminants that are present in the water. No water, irrespective of the original source, should be assumed to be completely free of contaminants. The most common process used for treatment of surface water and ground water consists of sedimentation, coagulation, filtration, disinfection, conditioning, softening, fluoridation, removal of tastes and odors, corrosion control, algae control, and aeration. Safe drinking water is best.
Sedimentation allows any coarse particles to settle out. Coagulation consists of forming flocculent particles in a liquid by adding a chemical such as alum; these particles then settle to the bottom. Filtration, as the name implies, is the passing of the water through a porous media; the amount of removal is a function of the filtering media. Disinfection kills most harmful organisms and pathogenic bacteria—chlorine is the most commonly used disinfecting agent. Softening means removal of materials that cause “hardness,” such as calcium and magnesium. Corrosion is an electrochemical reaction in which metal deteriorates when it comes in contact with air, water, or soil.
Drinking Water Treatment for Municipalities
In a typical municipal water treatment process, water flows through pumps to a rapid mix basin, then to a flocculation basin, to a settling basin, through filters to a clear well, then after disinfection, to storage tanks, and finally to the end users.
In areas that derive their water from rivers, pumps must be used since rivers are usually in low areas. Water enters the treatment plant at what is called the rapid-mix basin, where aluminum sulfate, polyelectrolytes, polymers, or lime and furic chloride are added as coagulants. The water flows next to the flocculation basins, where the coagulant mixes with the suspended solids. The coagulant is used to form suspended solids into clumps, or floc, which then settle out of the water. Floc forms when the particles from small solids gather to form larger particles. The water then slowly flows through settling basins where the floc settles from the water. Activated carbon is then added to the water to remove color, radioactivity, taste, and odor. Filtration then removes bacteria and turbidity from the water as it removes any remaining suspended solids and the activated carbon.
The water then enters a clear well, where additional chlorine is added to kill any pathogens which may be present. A minimum free-chlorine residual of at least 0.2 ppm is recommended in plants requiring sanitary protection through the whole water distribution system. In water supplies that are fluoridated, 1 milligram per liter of fluoride is added.
At this stage in the process, the water is potable, palatable, and ready for consumption. The water is moved into elevated tanks for storage through pumps. The water flows down from these tanks into the community.
Raw water and post-treatment water are tested for bacterial, physical, and chemical standards, particularly pH, color, and turbidity. The Safe Drinking Water Act of 1974 established maximum contaminant levels, which are the national drinking water standards. These apply to any water distribution system that serves at least twenty-five units daily. Standards may vary from state to state, but they cannot be lower than those prescribed by the federal government.
Drinking water quality
Many water quality problems can now be treated in the home with water filters, distillers, softeners, reverse osmosis units, and chemical units. Being an educated consumer will help you choose a home treatment system for your specific water quality problems and allow you to interact knowledgeably with salespeople and water treatment specialists.
If more than one water quality problem exists, choosing a treatment device can be especially confusing and complicated. Many times you cannot treat one problem without treating another first. Sometimes, two problems can be eliminated with one treatment. And, occasionally the treatment itself causes other problems.
For example, it is impractical to install a distiller to remove lead from your drinking water if your water is corrosive and continues to remove lead from the housepiping system. Similarly, a reverse osmosis unit installed to remove a pesticide contaminant will not work efficiency if the water also contains particles of insoluble minerals which can clog the membrane filter.
Depending on your source of water, you may have to correct minor problems before you can address your concern. The following guidelines for water treatment are based on the fact that it is practical and efficient to treat some water quality problems before others. For instance, only after turbidity, acidity, hardness and iron have been controlled will activated carbon filters, reverse osmosis units, or distillers operate efficiency.
Remember, these steps are a simplification of water treatment. When considering home water treatment, consult with water treatment professionals at a reputable and certified dealership to determine the best treatment approach for your particular problem.
Drink Water that is Safe drinking water.
Water Treatment Steps
- Have water tested for contaminants.
- Remove fine sand, silt, clay and other particles, using a mechanical filter or sedimentation.
- Treat bacterial contamination, using chlorination or other forms of disinfection.
- Remove hydrogen sulfide gas and other odor-causing substances, using chlorination, an oxidizing filter, or activated carbon.
- Remove insoluble iron and manganese particles using:
- a mechanical filter
- a water softener, for small amounts of dissolved iron and manganese
- an oxidizing filter for higher amounts of dissolved iron and manganese
- a chlorinator followed by a mechanical filter or an activated carbon filter for very high amounts of dissolved iron and manganese.
- Treat for hardness using a water softener.
- Neutralize acidity using a neutralizing filter.
- Remove volatile organic chemicals, trihalomethanes, certain pesticides and radon, using an activated carbon filter.
- Remove heavy metals, such as lead, mercury, arsenic, or cadmium, with reverse osmosis units or a distiller.
Glossary of Water & Wastewater Terms
Click on the letters below to find the word you are looking for.
- Absorb – To soak up or take in.
- Acidic – Containing an excess of acids, or hydrogen ions (H+) Having a pH less than 7. The opposite of basic. A lemon is acidic.
- Activated Sludge – Sludge floc produced in raw or settled sewage by the growth of bacteria and other organisms in the presence of dissolved oxygen.
- Activated Sludge Process – A biological sewage treatment process in which a mixture of sewage and activated sludge is agitated and aerated. Activated sludge separates from the treated sewage by settling and is disposed of or returned to the process as needed. The treated wastewater overflows to the next treatment stage.
- Aeration – Contact between air and a liquid by diffusion or mechanical mixing.
- Aerobic Bacteria – Bacteria which require oxygen for their growth.
- Agar – A gel-like substance containing nutrients used for growing bacteria for study.
- Alkaline – Also referred to as basic. Having a pH greater than 7. The opposite of acid. i.e. Dishwashing detergent
- Ammonia – A chemical which combines with chlorine in the water treatment process to form chloramine, a long-lasting disinfectant.
- Anaerobic Bacteria – Bacteria which grow in the absence of oxygen and get oxygen from breaking down complex substances.
- Aquifer – Any formation of rock that contains water. Usually underground and formed by layers of soil and rock. May supply water to a well or a spring.
- Atmosphere – The layer of gases surrounding the earth.
- Bacteria – Single-cell microorganisms occurring naturally almost everywhere. They range from beneficial, to harmless, to deadly. Too small to be seen with the naked eye.
- Basic – Also referred to as alkaline. Having a pH greater than 7. The opposite of acid. i.e. Dishwashing detergent
- Biochemical Oxygen Demand – (BOD) The quantity of oxygen utilized in the metabolism of organic matter in a specified time and at a specified temperature. It is determined by the availability of a material as a biological food and by the amount of oxygen utilized by the microorganisms during oxidation.
- Buffer – A substance that alters the pH of a solution by neutralizing acids and bases. This process is called ‘buffering.’
- Carbon Activated – Carbon powder is added to the water treatment process to absorb taste and odor, most often in the spring.
- Chloramine – A long-lasting disinfectant formed by ammonia and chlorine, A small amount of the disinfectant remains in the drinking water to kill any bacteria in the pipes running between the water treatment plant and your home.
- Chlorine – A liquid or gas chemical used to disinfect water. Chlorine can destroy harmful microorganisms and reduce some tastes and odors in water.
- Cholera – A dangerous disease caused by a type of bacteria that causes intestinal disorders. This bacterium is often found in untreated water.
- Clarifier – Drinking water is treated in clarifiers which look like huge swimming pools. Clarifiers are used to settle out dirt and alum sludge.
- Colonies – A group of the same kind living or growing together. i.e. Bacteria colony
- Conservation – Keeping, protecting or preserving a resource. Using natural resources wisely.
- Contaminant – Anything added to a substance that makes the substance unfit for use. i.e. motor oil is a contaminant in drinking water but not for a car engine.
- Cross Connection – A connecting pipe in plumbing, through which drinking water could be contaminated, polluted, or infected.
- Cyst – A microorganism with a tough protective covering.
- Decomposition of Sewage – The break down of the organic matter in sewage through aerobic and anaerobic bacterial processes.
- Denitrification – The reduction of nitrates in a solution by biochemical action.
- Detention Time – The theoretical length of time for water to pass through a basin or tank, if all the water moves with the same speed.
- Digester – A tank in which the solids from sewage sedimentation are stored to allow total aerobic or anaerobic decomposition to occur.
- Dilute – To water down and make less concentrated.
- Disinfectant – A substance used to purify water by removing or killing contaminants.
- Dissolved Oxygen – (DO) The amount of oxygen dissolved in sewage, water, or any other liquid. Usually expressed in mg/L or percent of saturation.
- Distillation – A process used to purify water by evaporation; boiling it and then collecting the steam as it condenses. Most pollutants remain in the unevaporated water.
- Dysentery – A disease caused by a type of bacteria, characterized by severe diarrhea and loss of body fluids.
Drinking water for commercial companies
- Ecosystem – All the living and non-living things that interact together in a given area.
- Effluent – Liquid waste discharged into the environment. i.e. sewage, liquid industrial waste or smoke.
- Eutrophication – The process by which a pond or lake becomes rich in dissolved nutrients. This encourages growth of oxygen-depleting plant life, resulting in harm to other organisms. Pollutants such as sewage and fertilizers speed up the process.
- Evaporation – The process by which water becomes vapor in the atmosphere.
- Facultative – Bacteria organisms having the capacity to live under multiple environmental conditions (aerobic vs. anaerobic).
- Filter – A screening device or porous substance used to remove solid material from liquids. Filters, made out of a layer a coal and a layer of sand, trap dirt or bacteria in the water treatment process.
- Floc – The chemical alum attracts dirt and silt particles to form larger particles called floc. Floc looks like big snowflakes floating in water which settle in the clarifiers and are later removed as sludge.
- Flotation – A method of raising suspended matter to the surface of the liquid in a tank as scum – by aeration, the evolution of gas, chemicals, electrolysis, heat, or bacterial decomposition – and the subsequent removal of the scum by skimming.
- Fluoride – A chemical compound added to drinking water to help prevent cavities.
- Food Chain – The transfer of energy from its primary source (plants) to larger animals.
- Food Web – An interlocking pattern of food chains.
- Fungus/Fungi – Plants lacking chlorophyll (green pigment) which include yeasts, molds, smuts and mushrooms.
- Giardia – A parasitic microorganism carried by animals in the form of a cyst. It is spread in animal feces and causes a disease commonly known as Beaver Fever.
- Grit – The heavy mineral matter in water or sewage, such as gravel.
- Incubator – A small oven-like appliance that is used to heat and grow bacteria samples.
- Intake – The point where water enters a channel or pipe into a treatment plant.
- Irrigate – To water agriculture crops.
- Microorganism – Small living creatures that you need a microscope to see, i.e. bacteria, protozoa and algae.
- Mixed Liquor – A mixture of activated sludge and sewage in the aeration tank undergoing activated sludge treatment.
- Molecule – The smallest physical unit of an element or compound, consisting of one or more atoms.
- Nitrification – The oxidation of ammonia nitrogen into nitrate through biochemical action.
- Non-Point Source – Pollution which enters the environment from a non-specific site. This is the most common form of water pollution and the most difficult to control. It includes runoff from farms, logging operations, construction sites, golf courses, landfills, gardens, streets and parking lots.
- Oligotrophic – Lakes that are abundant in oxygen and contain few plant nutrients. Water is usually clear with little weed or algae growth. Mountain lakes are often oligotrophic.
- Organic – Pertaining to, or derived from living organisms.
- Ozone – Three molecules of oxygen bound together – 03. The oxygen we normally breathe has 2 molecules of oxygen bound together – 02. Ozone is used as a disinfectant in some water treatment plants.
- Pathogenic – Something which can cause disease.
- pH “power of Hydrogen” – On the pH scale, a reading of 7 is neutral. Below 7 is acidic with lower numbers indicating greater acidity. Above 7 is basic, with higher ratings showing higher alkalinity. Lemons, for example, are acidic and many detergents are basic.
- Photosynthesis – The process plants use to get energy from the sun. Plants use the sun’s energy and the chlorophyll (green stuff) found in their leaves to produce the food they need to live.
- Point Source – Pollution entering the environment at a specific site, i.e. a factory discharging effluent into a river or a person dumping used motor oil down a storm sewer.
- Pollutant – Anything added to a substance that makes the substance impure. i.e. motor oil in drinking water.
- Precipitation – Water from rain, hail, sleet, or snow.
- Pump – Mechanical device allowing water to be lifted or raised.
- Reservoir – A storage tank holding one to two days’ supply of drinking water.
- Resource – A valuable supply of natural materials, i.e. oil, water, coal and trees.
- Riparian – Land bordering a river, lake or stream.
- Runoff – Rain or melted snow which is not absorbed into the soil, but flows across land into streams, lakes and rivers.
- Screen – A device for removing large suspended or floating debris from wastewater.
- Sector – Part of a society or a nation’s economy, i.e. the housing sector, the education sector.
- Sediment – Matter which settles to the bottom of a tank, pond, river or ocean.
- Sedimentation – The process by which particles suspended in water are allowed to settle to the bottom of a lake, river or container. Dirt, solid minerals and some bacteria are removed from drinking water through the sedimentation process.
- Sewage – Solid and liquid waste including human feces and urine.
- Sewage Treatment, Tertiary – Additional treatment of biologically treated sewage to reduce nutrients or other constituents.
- Sewer – A pipe carrying wastewater or drainage water.
- Sludge – Floc (alum + dirt) or calcium carbonate settled on the bottom of a water treatment clarifier it is called sludge. It is also the accumulated settled solids deposited from sewage in tanks or basins, and containing water to form a semi liquid mass. The sludge is removed and disposed of.
- Sludge Volume Index – (SVI) The volume in milliliters occupied by one gram of dry solids after the aerated mixed liquor settles 30 minutes.
- Stakeholder – Person or group with an investment or interest in something such as a business or industry.
- Surface Water – Water on the surface of land, such as rivers, lakes, and ponds.
- Sustainable – Extracting natural resources without destroying the ecological balance of an area, i.e. sustainable development.
- Transpiration – The process by which green plants give off water through pores in their leaves. Water is a by-product of the photosynthesis process.
- Turbidity – The amount of solid material floating in water. It may be organic (from plants and animals) or inorganic (silt and clay).
- Typhoid – A potentially fatal intestinal disease. Bacteria usually enter a human’s body in food or drink. In Canada and the United States, typhoid from water sources has been brought under control by filtration and chlorinating.
- Ultraviolet – (UV) Exposing drinking water or wastewater to ultraviolet light to deactivate harmful microorganisms ability to reporoduce, rendering them harmless.
- Waste Stabilization Pond – (or Lagoon) Any pond, natural or artificial, receiving raw or partially treated sewage or waste, in which stabilization occurs through sunlight, air and microorganisms.
- Wastewater – Water from homes and businesses that flows down the drain or toilet.
- Water Meter – An instrument for measuring the quantity of water flowing into a building.
- Water Treatment – A method of cleaning water for a specific purpose, such as drinking.
- Water Vapour – The gaseous state of water.
- Watershed – The entire region draining into a river, river system or body of water.
- Well – A pit, hole, or shaft dug into the earth to tap an underground supply of water.