Sources and Impurities of Water
Definition
Water sources are the natural or artificial places from which water is obtained, such as rainwater, rivers, lakes, wells, springs, and seas. Impurities of water are unwanted substances present in water in dissolved, suspended, colloidal, or biological form that reduce its purity and may make it unsuitable for specific uses.
Main Content
1. Sources of Water
Atmospheric sources
- Rain, snow, and hail are the primary natural sources of water. Rainwater is the purest natural form of water, but while falling through the atmosphere it may absorb gases like carbon dioxide, sulfur dioxide, and nitrogen oxides, making it slightly acidic. It may also collect dust, smoke, and microorganisms.
Surface and underground sources
- Surface water includes rivers, lakes, ponds, reservoirs, and streams. These are widely used for domestic and industrial supply but are more prone to contamination from sewage, industrial waste, agricultural runoff, and decaying organic matter. Groundwater is obtained from wells, tube wells, and springs. It is generally clearer and less contaminated because soil acts as a natural filter, but it often contains dissolved minerals such as calcium, magnesium, iron, and chlorides.
2. Types of Impurities in Water
Physical impurities
- These are visible or measurable impurities such as suspended particles, clay, silt, sand, algae, and turbidity. They affect the appearance and clarity of water. Turbid water is undesirable in drinking water and industrial processes because it may clog pipes, reduce efficiency, and interfere with treatment.
Chemical and biological impurities
- Chemical impurities may be dissolved salts, gases, acids, alkalis, heavy metals, pesticides, and organic compounds. For example, excess fluoride can cause fluorosis, and nitrates can be harmful to infants. Biological impurities include bacteria, viruses, protozoa, and worms, which may cause waterborne diseases such as cholera, typhoid, dysentery, and hepatitis.
3. Classification of Water Contaminants by Origin
Natural impurities
- These occur naturally through contact with rocks, minerals, air, and biological decay. Examples include dissolved calcium salts causing hardness, dissolved iron causing reddish stains, and dissolved carbon dioxide making water acidic. Natural impurities are common in both surface and groundwater.
Man-made impurities
- These are introduced by human activities such as domestic sewage discharge, industrial effluents, mining, fertilizer and pesticide use, oil spills, and urban waste disposal. These contaminants may include detergents, dyes, phenols, acids, toxic metals like lead and mercury, and pathogens from sewage. Man-made impurities are often more dangerous because they can be highly toxic and difficult to remove.
Working / Process
1. Collection of water from sources
- Water is obtained from rain, rivers, lakes, ponds, wells, boreholes, springs, or seawater depending on availability and purpose. The quality of water varies greatly with source. For example, river water may contain more suspended matter, while groundwater may contain more dissolved salts.
2. Entry and accumulation of impurities
- As water moves through the environment, it dissolves gases from air, leaches minerals from soil and rocks, and carries impurities from human and natural activities. During surface flow, it picks up dust, organic debris, microorganisms, oils, and chemical pollutants; underground flow adds minerals and may also carry dissolved gases like carbon dioxide and hydrogen sulfide.
3. Assessment and treatment need
- Water is analyzed for physical, chemical, and biological impurities to determine its suitability for use. Depending on the contaminants present, it may require sedimentation, filtration, disinfection, softening, aeration, activated carbon treatment, or advanced purification methods such as ion exchange, reverse osmosis, and distillation.
Advantages / Applications
Helps in selecting proper water treatment methods
- Knowing the source and nature of impurities allows engineers to choose suitable purification techniques for drinking water, boiler feed water, cooling water, and industrial processes.
Improves public health and safety
- Identifying harmful impurities helps prevent waterborne diseases and toxic effects caused by contaminants like pathogens, heavy metals, and excess dissolved chemicals.
Supports industrial efficiency and product quality
- In industries such as textiles, pharmaceuticals, food processing, power generation, and chemical manufacturing, water quality directly affects equipment life, product purity, and process performance.
Summary
- Water comes from atmospheric, surface, and underground sources, and each source has different impurity characteristics.
- Impurities in water may be physical, chemical, or biological, and they can be natural or man-made.
- Understanding water sources and impurities is essential for safe use, effective treatment, and industrial applications.
- Important terms to remember: rainwater, surface water, groundwater, turbidity, dissolved salts, hardness, pathogens, contaminants