Water / Natural/raw Water
Water is a transparent, tasteless, odorless, and nearly colorless liquid that forms the basis of
all living organisms on earth. It is composed of hydrogen and oxygen (H₂O) and exists in
different forms such as solid (ice), liquid, and gas (water vapor). Water is essential to life.
Without it, the biosphere that exists on the surface of the earth would not be possible.
Raw water refers to untreated water that originates/having its source from natural
environments such as rivers, lakes, reservoirs, groundwater, and rainwater. It contains
various dissolved and suspended substances, including minerals, organic matter,
microorganisms, and pollutants.
Categories of water
1. Potable water: It is safe to drink, pleasant to taste, and usable for domestic purposes
2. Palatable water: It is aesthetically pleasing; it considers the presence of chemicals that do
not cause a threat to human health
3. Contaminated (polluted) water: It is that water containing unwanted physical, chemical,
biological, or radiological substances, and it is unfit for drinking or domestic use.
4. Infected water: It is contaminated with pathogenic organism.
Composition of Raw Water
Raw water contains a variety of physical, chemical, and biological components, which
influence its quality and suitability for use. These components include:
Physical Composition
✓ Suspended Solids: Particles like silt, clay, sand, and organic debris.
✓ Turbidity: The cloudiness of water caused by suspended solids.
✓ Color: Due to dissolved organic matter or inorganic compounds like iron.
✓ Odor and Taste: Can result from natural substances, industrial discharges, or biological
activity.
✓ Temperature: Varies based on location, environment and climatic conditions
Temperature: Temperature is a measure of the average energy (kinetic) of water molecules. It
is measured on a linear scale of degrees Celsius or degrees Fahrenheit. Temperature is a basic
water quality variable. It determines the suitability of water for various forms of aquatic life.
Depending on the geographic location the mean annual temperature varies in the range of 10
to 30oC with an average of 16oC. Temperature affects a number of water quality parameters
such as dissolved oxygen.
Color: Color in water is primarily a concern of water quality for aesthetic reason. Colored water
gives the appearance of being unfit to drink, even though the water may be perfectly safe for
public use. Color of the water body can indicate the presence of organic substances, such as
algae or humic compounds. In recent times, Color has been used as a quantitative assessment
of the presence of potentially hazardous or toxic organic materials in water. Color is vital as
most water users, be it domestic or industrial, usually prefer colorless water. Determination
of Color can help in estimating the costs related to discoloration of the water. Color is reduced
or removed from water through the use of coagulation, settling and filtration techniques
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Taste and Odor: Taste and odor are human perceptions of water quality. Human perception of
taste includes sour (hydrochloric acid), salty (sodium chloride), sweet (sucrose) and bitter
(caffeine). Odor is produced by gas production due to the decomposition of organic matter or
by substances added to the wastewater. Odor is measured by special instruments such as the
Portable H2S meter which is used for measuring the concentration of hydrogen sulfide.
Turbidity: Turbidity is a measure of the light-transmitting properties of water and is comprised
of suspended and colloidal material. It is important for health and aesthetic reasons.
Transparency of natural water bodies is affected by human activity, decaying plant matter,
algal blooms, suspended sediments, and plant nutrients. Turbidity provides an inexpensive
estimate of total suspended solids (TSS) concentration.
Solids: Total dissolved solids (TDS) is used to describe the inorganic salts and small amounts
of organic matter present in solution in water. The principal constituents are usually calcium,
magnesium, sodium, and potassium cations and carbonate, hydrogen carbonate, chloride,
sulfate, and nitrate anions. Solids are classified as settle-able solids, suspended solids and
filterable solids.
Chemical Composition
✓ Dissolved Minerals: Such as calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), potassium
(K⁺), sulfate (SO₄²⁻), chloride (Cl⁻), and bicarbonates (HCO₃⁻).
✓ Organic Matter: Includes plant debris, algae, and humic substances from decayed
vegetation.
✓ Nutrients: Such as nitrogen (N) and phosphorus (P), which can promote algal growth.
✓ Heavy Metals: Examples include lead (Pb), mercury (Hg), arsenic (As), and cadmium
(Cd), chromium (Cr), nickel (Ni), copper (Cu), cobalt (Co) which can be toxic.
✓ pH: The acidity or alkalinity of water, usually ranging between 6.5 and 8.5 in natural
waters.
✓ Dissolved Gases: Oxygen (O₂), carbon dioxide (CO₂), hydrogen sulfide (H₂S).
pH: pH is a measure of how acidic or basic (alkaline) the water is. It is defined as the negative
log of the hydrogen ion concentration. The pH scale is logarithmic and ranges from 0 (very
acidic) to 14 (very alkaline). For each whole number increase (i.e. 1 to 2) the hydrogen ion
concentration decreases tenfold and the water becomes less acidic. The range of natural pH in
fresh waters extends from around 4.5, for acid, peaty upland waters, to over 10.0 in waters
where there is intense photosynthetic activity by algae.
Electrical Conductivity: The conductivity of water is an expression of its ability to conduct an
electric current as a result of breakdown of dissolved solids into positively and negatively
charged ions.
Salinity: Salinity is a measure of the number of salts in the water. Because dissolved ions
increase salinity as well as conductivity, the two measures are related. The salts in sea water
are primarily sodium chloride (NaCl). However, other saline waters owe their high salinity to
a combination of dissolved ions including sodium, chloride, carbonate and sulfate.
Alkalinity: The alkalinity of natural water is generally due to the presence of bicarbonates
formed in reactions in the soils through which the water percolates. It is a measure of the
capacity of the water to neutralize acids and it reflects its buffer capacity. Alkalinity in streams
is influenced by rocks and soils, salts, certain plant activities, and certain industrial
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wastewater discharges. Low nutrient (oligotrophic) lakes tend to have lower alkalinity while
high nutrient (eutrophic) lakes have a tendency of higher alkalinity.
Hardness: Hardness is a natural characteristic of water which can enhance its palatability and
consumer acceptability for drinking purposes. The hardness of water is due to the presence
of calcium and magnesium minerals that are naturally present in the water. The common signs
of a hard water supply are poor lathering of soaps and scum.
The following is a measure of hardness (expressed in mg/l as CaCO3):
Soft: 0 – 100 mg/l as CaCO3
Moderate: 100 – 200 mg/l as CaCO3
Hard: 200 – 300 mg/l as CaCO3
Very hard: 300 – 500 mg/l as CaCO3
Extremely hard: 500 – 1,000 mg/l as CaCO3
Heavy Metals: Heavy metal refers to any metallic chemical element that has a relatively high
density and is toxic or poisonous at low concentration notably mercury (Hg), cadmium (Cd),
arsenic (As), chromium (Cr), nickel (Ni), copper (Cu), cobalt (Co) and lead (Pb) etc. These are
the natural components of geological environment. They enter the human body via food,
drinking water and air to small extent.
Dissolved Oxygen: Dissolved oxygen is the amount of gaseous oxygen (O2) dissolved in an
aqueous solution. It gets into water by diffusion from the surrounding air, by aeration (rapid
movement), and as a waste product of photosynthesis. The oxygen in dissolved form is
needed by most aquatic organisms to survive and grow.
Biochemical Oxygen Demand (BOD). Biochemical oxygen demand is the amount of dissolved
oxygen required by aerobic biological organisms to degrade the organic material present in a
water body at certain temperature over a specific time period. It widely used as an indication
of the organic quality of water and thus representing the pollution load. It is most commonly
expressed in milligrams of oxygen consumed per litter of sample during 5 days (BOD5) of
incubation at 20°C. When organic matter decomposes, microorganisms (such as bacteria and
fungi) feed upon this decaying material and eventually the matter becomes oxidized. The
harder the microorganisms work, the more oxygen will be used up giving a high measure of
BOD, leaving less oxygen for other life in the water.
Chemical Oxygen Demand. Chemical Oxygen Demand (COD) determines the quantity of
oxygen required to oxidize the organic matter present in water body under specific conditions
of oxidizing agent, temperature and time. COD is an important water quality parameter as it
provides an index to assess the effect discharged wastewater will have on the receiving
environment. Higher COD levels represent the presence of greater amount of oxidizable
organic material in the sample, the degradation of which will again lead to hypoxic conditions
in the water body. The ratio of BOD to COD indicates the percent of organic material in water
that can be degraded by natural microorganism in the environment.
Biological Composition
✓ Microorganisms: Such as bacteria (E. coli -Escherichia coli, Salmonella), viruses, protozoa,
and fungi.
✓ Algae: Different species, including cyanobacteria, which may produce toxins.
✓ Zooplankton: Tiny aquatic animals that feed on algae and organic matter.
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✓ Pathogens: Disease-causing microbes (Giardia, Cryptosporidium, Cyclospora) that pose
health risks in untreated water.
E. coli is a bacterial species found in the fecal matter of warm-blooded animals (humans,
other mammals, and birds). Total coliform bacteria are an entire group of bacterial species
that are generally similar to and include the species E. coli. There are certain forms of coliform
bacteria that do not live-in fecal matter but instead live-in soils. Total coliform bacteria, fecal
coliform bacteria, and E. coli are all considered indicators of water contaminated with fecal
matter.
Water treatment
The process of treating raw water (surface or groundwater) to make it suitable for human
consumption or industrial use. Water treatment is the process of removing biological,
chemical, and physical contaminants from water to make it safe, clear, and suitable for human
consumption, domestic use, and industrial applications. It involves purifying water by
removing pollutants, pathogens, and harmful substances so as to improve its quality with the
purpose of serving an end-use. The most common end-uses include drinking water, industrial
water supply, water recreation, and for replenishing environmental sources, such as rivers
and lakes.
Why water treatment?
1. Water in its natural state is rarely pure due to the presence of natural impurities. Natural water
sources contain impurities such as dissolved minerals, organic matter, microorganisms,
and pollutants. These impurities come from geological formations, atmospheric
deposition, and human activities. Proper treatment is necessary to make water safe and
suitable for use.
Water in its natural state is rarely pure and of high quality due to interaction with the various
environmental spheres which contain impurities. These impurities come from natural processes, human
activities, and geological formations which affect its physical, chemical, and biological quality, making
it unsuitable for direct consumption or industrial use without treatment.
➢ Atmospheric interaction. As water moves through the atmosphere, it evaporates from
oceans, lakes, and rivers, then condenses and falls as precipitation. During this process, it
absorbs atmospheric gases such as carbon dioxide (CO₂), oxygen (O₂), nitrogen (N₂), and
sulfur dioxide (SO₂). The dissolved CO₂ forms carbonic acid (H₂CO₃), making rainwater
slightly acidic. Industrial emissions release sulfur oxides (SOₓ) and nitrogen oxides (NOₓ),
which contribute to acid rain, further contaminating natural water sources.
➢ Geologic formation. As water moves through soil, rocks, and underground aquifers, it
dissolves minerals such as calcium (Ca²⁺), magnesium (Mg²⁺), iron (Fe²⁺), and arsenic (As).
These minerals contribute to water hardness, which affects its suitability for drinking,
domestic, and industrial use. In some regions, toxic elements like arsenic and fluoride
naturally contaminate groundwater.
➢ Microorganisms and organic activity. Natural water sources contain bacteria, viruses,
protozoa, and algae originating from soil, decaying plants, and animal waste. Some
microorganisms, such as Escherichia coli (E. coli), Salmonella, Giardia, and
Cryptosporidium, are harmful and can cause serious waterborne diseases. Algae growth
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in lakes and reservoirs can produce toxins, affecting water quality and making it unsafe
for consumption, hence making water impure.
➢ Runoff. Rainfall causes surface runoff, which picks up pesticides, herbicides, fertilizers,
and industrial chemicals from agricultural and urban areas. Agricultural runoff
introduces nitrates and phosphates, which promote eutrophication, leading to excessive
algal blooms that deplete oxygen levels in water bodies. Urban runoff from roads,
factories, and landfills introduces oil, heavy metals (e.g., lead and mercury), and plastics,
which degrade water quality. These contaminants therefore make surface and
underground water rarely pure.
2. To protect the consumer’s health. Untreated water may contain harmful bacteria, viruses, and
chemicals that can cause diseases like cholera, typhoid, and dysentery. Water treatment
removes these contaminants, ensuring that consumers have access to clean and safe
drinking water. This helps prevent waterborne illnesses and supports public health.
3. To make water acceptable. Water should be clear, colorless, tasteless, and odorless to be
considered acceptable for consumption and other uses. Impurities such as sediments,
algae, and dissolved gases can affect water’s aesthetic qualities. Treatment processes like
filtration and aeration improve water clarity, taste, and smell.
4. To protect the supply and distribution installations. Impurities in water, such as suspended
solids, dissolved salts, and biological growth, can cause pipe corrosion, scaling, and
blockages in distribution systems. Proper treatment prevents damage to water
infrastructure, reducing maintenance costs and ensuring reliable water supply.
5. To improve water quality for industrial and domestic use. Industries require water free from
sediments, dissolved minerals, and biological contaminants to prevent equipment
damage and ensure product quality. Similarly, households need treated water for cooking,
cleaning, and hygiene. Water treatment ensures a reliable supply of clean water for
various applications.
