What is impurity in water?

water purity

Water not only quench your thirst but, it also plays a vital role in building a healthy immune system, healthy metabolism and even helps in flushing out toxins from the body. 

Water as we have studied since our school days comprises of 2 molecule of hydrogen and 1 molecule of oxygen. Pure water (H20) is colorless, tasteless, and odorless. 

That’s water in the purest form free from any dissolved salts or gases. One of such common form of pure water is distilled water.

1. What are impurities in water?

Water in pure form is not available and often it contains of various organic, inorganic salts and other biochemical impurities. Example of some of the inorganic salts which are found in water are calcium, magnesium, potassium and sodium, which are all cations, and carbonates, nitrates, bicarbonates, chlorides and sulphates, which are all anions.

These minerals get mixed with water either through natural process or as consequences of industrialisation or use other human activity.  

Water known as “universal solvent” can dissolve every naturally occurring substance on the earth. 

Ground water usually gets minerals from the earth crust, soil. Surface water or water available in water bodies like lake, canal, river, pond etc gets minerals from earth surface and also from industrial waste.

Biological contamination of water is caused by the presence of micro organisms like algae, bacteria, protozoa, pathogens, microbes, Viruses, Parasites and their eggs (cysts), etc. commonly called ‘germs’. The health effects of drinking water contaminated with germs may be severe.

So impurities in water may be classified in three categories

  • Physical impurity (TDS, TSS, color, odor, taste etc.)
  • Chemical impurity (pH, Hardness, Alkalinity, COD, BOD, pesticides etc.)
  • Microbiological impurity (E. coli, coli form, toxicity taste, plate count etc.)

2. Does it mean that water containing mineral is impure?

That’s not so straightforward. Purity of water is often taken as purity in sense of drinking. Drinking water is allowed to have a permissible range of some of the minerals which are essential in growth of human body.

Whereas, there are minerals which are harmful for our body and must not be present in water. Heavy metals and Minerals like Nitrates, Fluorides, Lead,cadmium and Arsenic are not at all permissible in pure water. Heavy metals once consumed is not excreted or removed from the body but keeps on accumulating in the body. 

3. Distilled water Vs pure water Vs pure drinking water

Distilled water is water that has been boiled into vapour and condensed back into liquid in a separate container. Impurities in the original water that do not boil below or near the boiling point of water remain in the original container.

Purified water is water that has been mechanically filtered or processed to remove impurities and make it suitable for use. 

Distilled water has been the most common form of purified water till a long time, but modern processes like Reverse osmosis, Ultra filtration, Micro filtration, UV filtration is able to produce highly purified water that has many uses, largely in the production of medications, laboratories, Industries etc.

Pure Drinking water is water that is safe to drink or to use for food preparation. Water in general may contain impurity in form of physical, chemical or biological parameter. Any water having these parameter values under permissible range is pure drinking water.

4. Can we drink distilled water?

You can but that’s not a pure drinking water. Distillation removes all minerals from water. This results in demineralized water, which is not healthier compared to pure drinking water.

The World Health Organisation investigated the health effects of demineralized water in 1980, and its experiments in humans found that demineralized water increased diuresis.

5. What is Turbidity in water?

Turbidity is a measure of the degree to which the water loses its transparency due to the presence of suspended particulates.The more total suspended solids in the water, higher is the turbidity.

There are various parameters influencing the cloudiness of the water. Some of these are:

  • Phytoplankton
  • Sediments from erosion
  • Waste discharge
  • Algae growth
  • Urban runoff

You would have notices turbidity in surface water sources like river, canal, lakes etc. These need to be purified physically, chemically and biologically.

6. How does turbidity affect quality of water?

The suspended particles in water with turbidity absorb heat from the sunlight, making turbid waters become warmer, and so reducing the concentration of oxygen in the water.

7. Why supply water smells and looks colored in monsoon?

During rainy season, the run-off rainwater washes off land pollutants along with eroded top soil, sewage, industrial and agricultural wastes and sediments to the river stream.

These contaminants increase the bacterial load in water. Hence, more bleaching powder (more than the permissible limit) is added to the water to reduce high bacterial population. This activity triggers the formation of chlorine by-products in water.

8. How to ensure intake of pure water in home?

The first and foremost task is to get water tasted, if you have not done that. Simple test like TDS test can be done at home also through devices available online.

You can read this article on TDS to gain detailed idea : What is TDS and how to check TDS of water at home?

Having a good quality water purifier at home is essential if water supply in your home is not of good standard. Even some municipal water supply which though claims that are suitable for drinking should be purified with suitable purifier first before usage. Because municipal water may get contamination from tank, corrosion in pipe.

Here is your Water Purifier buying guide : How to buy best water purifier for my home.

Water tanks may become breeding ground for microbes in water if not properly maintained. In water test for microorganisms, presence of bacteria known as Coliform or e-coli is tested. This is because it is the most common species, and the first microorganism to infect water.

For biological purification you can choose either membrane purification (Ultra filtration) or UV purification water purifier. Membrane purification of water actually filters out all bacteria from water where as UV water purifier which kill bacteria in water but leaves their bodies in the drinking water.


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