Everything You Need To Know About Water Quality

Water quality is the ability of a water source to meet the chemical, biological, and physical requirements of a specific water use. However, the Environmental Engineers set the standards of water quality.

Table of Contents

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Introduction To Water Quality

Pure water is that which contains two parts of hydrogen and one part of oxygen and nothing else. However, due to its molecular structure (hydrogen bonding) and electrical properties, which include a very high dielectric constant and low conductivity, water is capable of dissolving many substances.

Some compounds, like sugars and alcohols, are dissolved through hydrogen bonding; others, such as salts, which are ionised, are dissolved through neutralisation—ions of opposite charge by clusters of oriented water molecules.

Pure water is never formed in nature. Water drops just emitting from clouds may be considered pure, but as they fall, they contain gases and dust from the air that get dissolved in them, making the water impure. Reaching the ground, the rain water dissolves some minerals and salts, which flow.

Potability and Polatability of Water

Absolute purification of water is not required because certain dissolved salts are necessary for health, as they assist in food assimilation and make water tasteable.

To meet the general requirement, water supplies must possess the following two attributes, i.e. potability (wholesomeness) and palatability.

Potability (Wholesomeness)

Potability means health or favourable to health. Potable water must possess the following characteristics.

• Safe from infections: uncontaminated with disease-causing germs.
• Free from toxic (poisonous) substances and
• Free from excessive amounts of minerals and organic matter.

Polatability

Refers to agreeability through the senses of sight (e.g. colour and turbidity), taste, smell (odour), and touch (e.g. temperature). Potable water must possess the following:

• Free from odour, turbidity, and objectionable taste.
• Be of moderate temperature in summer as well as in winter.
• Be aerated.

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Degree of Purity of Water Based on Uses

The degree of purity of water also depends on its particular use. Water of good quality for one purpose may be considered to be of poor quality for some other purpose.

Thus, pure water is a relative term, and it must be interpreted with its use, as can be understood from the following general uses of a water-supply scheme.

1. Domestic uses

The water required must possess a high degree of purity. Drinking water and water used in the food industry and some other industries must meet the highest standard of purity.

A tolerance of a small degree of hardness developed due to certain dissolved salts is, however, permissible.

Potable (wholesome) water for domestic use should be:

• Clear (no suspended/ colloidal matter), odourless and colourless (i.e., aesthetically attractive).
• Free from harmful and disease-producing bacteria.
• Fresh and tasty.
• Unlikely to cause corrosion to pipes and other fittings.
• Free from harmful salts and other objectionable (i.e., toxic) substances.

2. Civic (or Public) uses

Washing of roads, cleaning (flushing) of sewers, etc. The nature of water allows some tolerable degree of impurity.

Thus, water containing suspended and dissolved impurities but not sewage or refuse may be used.

3. Commercial uses

The purity of water depends on the type of trade or business.

• Laundry should not be hard; otherwise, more soap will be consumed.
• For washing staple floors, they may contain some types of impurities.

4. Industries Use

Various chemical processes involved in the industry production need chemically pure water (e.g., food industries).

The nature of water required by different factories is so variable that some factories install their water supply plants, suiting their requirements.

Note: A city with well-developed and highly water-consuming industries should have two systems of water:

• One supplying potable water for domestic uses, and
• The other is for industrial uses.

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Impurities In Water

Types of Impurities

Common impurities may be classified into the following two main categories:

1. Based on the Solubility Potential of the Impurities

• Suspended impurities: These remain in suspension, i.e., they neither settle down nor get dissolved in water. It can be removed by the sedimentation process.
• Dissolved impurities: Their number may be very large because water is a very good solvent.
• Colloidal impurities: Colloids are particles in a finely divided form, which are neither in suspension nor in solution but in a condition midway between the two. Colloids are so small that ordinary settling tanks cannot remove them and are not visible. Colloids are electrically charged due to the presence of adsorbed ions on their surfaces. Acidic and neutral materials (e.g., silica, glass, and most organic material particles) have a negative charge, while particles of all basic materials (e.g., metallic oxides) are positively charged. The electrical charge present on the colloidal particles’ surface is so large compared to the mass of the particles. Thus, they repel each other, causing them to remain in motion permanently.

2. Based on the chemical Nature of Impurities

These category divides the impurities into three types as follows:

• Organic impurities
• Inorganic impurities
• Living impurities

Organic Impurities

There are natural and artificial organics, which may be in either suspended or dissolved form, as explained below:

Natural Organics

E.g., Dead animals and plant tissues. These types of impurities may be associated with colour, taste, odour, acidity, and harmful germs.

Artificial Organics

In some cases, these may be toxic or carcinogenic (causing, e.g., cancer).

Making examples on this:

• Chlorinated hydrocarbons used as pesticides and herbicides have been shown to produce carcinogenic effects.
• Trihalomethanes may enter water from industrial processes, but most are formed during the chlorination of water containing naturally occurring organics such as humic acid.
• Volatile Organic Chemicals (VOCs) are industrial chemicals that are widely distributed in both surface and ground waters. Many of these substances are either known or suspected to be carcinogens.

Inorganic Impurities

These impurities include both suspended and dissolved materials.

1. Suspend Inorganics

Include silt, clay, and mineral matters which are undesirable for aesthetic reasons (i.e., they cause turbidity, colour, and odour) but their primary effect on quality lies in their ability to shield micro-organisms from disinfectants.

2. Dissolved Inorganics

Those having health problems include Aluminium, arsenic, barium, lead, mercury, nitrate, selenium, and silver.

Dissolved organics:

• Aluminium: occurs naturally in some raw water and is commonly used as a coagulant in water treatment processes. The use of aluminium cooking utensils, particularly for “stewing acidic fruits”, results in greater aluminium intake. Causes neuropathological disorders as well as physiological problems. This has necessitated the use of iron salts instead of aluminium as a coagulant in water treatment processes.
• Arsenic: Groundwater may contain arsenic. Regular consumption of water with high concentrations of arsenic can lead to “skin pigmentation” and a variety of gastrointestinal, haematological, and renal disorders.
• Fluorides: Occur naturally in some waters, water drawn from the surface through some geological formations. Sometimes added to water from chemical wastes. They are beneficial if in small concentrations, as such water improves dental health and prevents the formation of dental caries.
• Nitrate: Occurs naturally in many soils and is thus found in most groundwaters and surface waters as well as through the utilisation of nitrogen fertilisers.
• Iron and Manganese: Although they don’t cause health problems, they do impart a noticeable, bitter taste to drinking water even at very low concentrations. They occur in groundwater as ferrous and manganous iron. When exposed to air, they are oxidised to stable insoluble ferric iron and manganic manganese, which make water turbid with a rust colour. They also cause brown/black stains on laundry and plumbing fixtures.
• Copper and Zinc: These are non-toxic when in small concentrations, and fact, both are beneficial and essential for human health. They cause undesirable tastes in drinking water; however, at high concentrations, zinc imparts a milky appearance to the water.
• Lead: Soft acidic waters from upland catchments are often highly “plumbosolvent” so that significant amounts of lead can be dissolved, particularly when standing in service pipes overnight. Lead is a cumulative poison, so continued exposure can eventually produce toxic effects. Chemical treatment of the water before distribution by the addition of lime (caustic soda) reduces the dissolution of lead. But removal of lead piping would probably be essential to meet the lead limit in water.
• Hardness: Increased hardness in drinking water up to about 175mg/l reduces the incidence of some forms of heart disease. Thus, softening of hard water could have a detrimental effect. It increases the sodium content of the water, which can be undesirable for patients suffering from some heart and kidney complaints.

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Living Organisms

The absence/presence of living organisms in water can be a useful indication of its quality. In streams, rivers, and lakes, the diversity of fish and insect species provides a measure of biological balance or health of the aquatic environment.

A wide variety of different species of organisms usually indicates that the streams or lakes are unpolluted.

1. Micro-Organisms

They play an essential role in the life processes of all living organisms, including humans. Most of the microbes are beneficial. Microorganisms such as yeasts contained in foods cause fermentation, producing Carbon dioxide and alcohol from sugar.

Some types of Organisms

• Bacteria: These are single-celled organisms. Since they are non-chlorophyllous, they can not make their food. Thus, they utilise soluble food taken through a rigid cell wall. Their usual mode of reproduction is by binary fission, although some species reproduce sexually or by budding. Most bacteria are harmless and, under certain conditions, are beneficial to human beings, animals, and plants. Such bacteria are called Non-pathogens. Others are harmful to health, causing serious waterborne diseases (e.g., cholera, typhoid, etc.) and are known as pathogens.
• Algae: These are microscopic, photosynthetic plants having neither roots, stems, nor leaves. They range from tiny single cells and easily noticeable when their numbers proliferate (grow) in water. Excessive growths of algae (called algae brooms) are unsightly. Free-floating algae are called phytoplankton. Some algae species are multicellular, growing as filaments that sometimes appear as green slime in water. Blue-green algae release toxins which can be fatal to animals and can produce skin irritation to humans in contact with the water, and may produce gastrointestinal illness if the water is ingested.

• Protozoa: They are single-celled microscopic aquatic animals that reproduce by binary fission (i.e., amoeba), and consume solid organic particles, bacteria and algae for food. They are, in turn, ingested as food by higher-level multicellular animals.
• Viruses: Are microscopic intracellular parasites that consist of a strand of genetic material, deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) with a protein coat. They cannot synthesise new compounds (i.e., they lack the metabolic system for their activity and self-reproduction). Instead, they invade the living host cells where the viral genetic material takes over the host cells’ metabolic processes for its use. Viruses of concern in water pollution are those found in the intestinal tracts of humans. They are excreted with the faeces from infected persons. The frequent means of transmission is from person to person by the faecal-oral route. The viruses can cause a variety of illnesses in humans, including chicken pox, rabies, yellow fever, polio, influenza, gastroenteritis, and the common cold.
• Fungi: These are microscopic aerobic multicellular, non-photosynthetic organisms that live on other plants or animals, which may be dead or alive.

2. Macro-Organisms

These are visible to the naked eye.

• Rotifers: These are simple multicellular aerobic animals that metabolise solid food. The name is derived from the fact that a rotifer has two sets of rotating cilia on its head, which are used for motility and capturing food.
• Macro crustaceans: Are multicelled animals (2mm size) that have branched swimming feet or shell-like covering with a variety of appendages.
• Worms: From the standpoint of human health, many worms are of great concern. They may be red or greyish. Red bloodworms are the larvae of chironomus flies, and others are larvae of small but allied midge flies. The adult lays eggs on the water surface in a basin/ reservoir. The eggs hatch into larvae, which attach themselves to the side walls.

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Diseases

Characteristics of Diseases

The main features of communicable diseases are as follows:

1. All diseases require the following for their spread: a source of infection, a transmission route, and exposure to susceptible living organisms.
2. Control of diseases is thus based on: curing sufferers, breaking the transmission route, and protecting the susceptible population.

Engineering measures in disease control are essentially concerned with breaking the transmission route, WHILE Medical measures are concerned with the other two parts of the infection chain.

Types of Diseases

1. Contagious Diseases

These are diseases in which the pathogen spends its life in the human body and can only live for a short time in an unfavourable environment outside the body. It is thus transmitted by direct contact, droplet infection, or similar means.

2. Non-Contagious Diseases

The pathogens spend part of their life cycle outside the human body, so that direct contact is not of great significance.

This type of disease may involve simple transmission routes with extra-corporal development of the infective organism taking place in soil or water.

In many cases, however, more complex transmission routes occur, requiring an intermediate host as part of the parasite’s development.

Please note:

When a disease is always present in a population at a low level of incidence, it is termed ENDEMIC. When a disease has widely varying levels of incidence, the peak levels are an epidemic, and worldwide outbreaks are termed a pandemic, such as the COVID-19 pandemic.

Water-Related Diseases

These are the diseases whose incidence can be influenced by water. May be due to viruses, bacteria, protozoa, or worms.

1. Waterborne Disease

The commonest form of water-related diseases and that which causes most harm on a global scale includes those diseases spread by contamination of water by human faeces or urine.

Infections occur when the pathogen organism gains access to water, which is consumed by a person who does not have immunity to the disease.

2. Water-washed Diseases

These include some skin and eye infections, which, whilst not normally fatal, have a serious debility effect on sufferers.

In case of poor hygiene, this type of disease is due to an inadequate water supply for washing. Water in this context is a cleansing agent.

Some of these diseases are ascariasis, conjunctivitis, diarrhoeal diseases, leprosy, scabies, skin sepsis, bacterial ulcers, and trachoma.

They tend to be associated with hot climates, and their incidence can be significantly reduced if ample water is available for personal washing.

3. Water-based Diseases

These are mainly caused by worms which infect the sufferers and produce eggs that are discharged in the face or urine.

Infection often occurs by penetration of the skin rather than consumption. Some of these diseases are schistosomiasis (also known as bilharzia or snail fever) and dracunculiasis (also known as Guinea worm disease).

4. Water-Related Insect Vectors

These are diseases which are spread by insects that breed or feed near water, so that their incidence can be related to the proximity of a suitable water source.

Infection with these diseases is in no way connected with human consumption of or contact with the water.

Some of these diseases include malaria, onchocerciasis (also known as river blindness), sleeping sickness, and yellow fever.

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Chemical-Related Illness

These are due to some chemical substances dissolved in natural water (which are potentially hazardous to human health).

The chemicals are mostly compounds used in agriculture, the home, and in industry, which can find their way into surface and groundwaters.

With chemically related health effects, they occur in two types as follows:

• Acute effects: where the consequences of consumption of the contaminated water are more or less immediately apparent, and
• Chronic effects: where continued ingestion of the contaminated water produces a long-term hazard.

Control Measures to Ensure Water Quality

Waterborne diseases can be controlled either by improving the microbiological quality of drinking water or by preventing the casual use of other unimproved polluted water.

The microbiological quality of drinking water could be improved by the treatment of water before use as follows:

• Chemical treatment, which includes Chlorination and coagulation of suspended particles.
• Physical treatment, which includes boiling, sand filtration and sedimentation.

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Final Thought On Water Quality

As you have seen in this post, water quality is a long topic. In short, it relates to the best way to obtain clean water for human consumption.

Continue with Water pollution and control, and later, I will continue with Water Quality analysis and a general assessment of water quality.

So don’t hesitate to come back later to see the continuation of this great post (water quality) topic.

That’s all.

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