Our planet, the Earth, contains around 75% of water. Our planet has high percentages of water in the liquid state, hence appears blue when seen from space. That is why it is also known as the blue planet.
Indeed it is the presence of water that separates our planet from the rest. Water is the crucial element of our very existence without which we could not survive for long. We come back from a jog, or a good workout and quickly grab a bottle of water to quench our thirst. But can we drink any water?
Of course, not! We can only drink water that has been filtered and treated chemically to remove impurities and harmful microbes so that it is safe to drink. Such water which is safe for human consumption is called potable water.
Fig. 1. Glass of water, Public domain, Wikimedia Commons
We will first introduce you to the definition of potable water by discussing what potable water contains.
Then, we will go over the sources from which potable water can be obtained.
We will then discuss the characteristics of potable water.
We will give you some examples of potable water.
Then, we will look into the characteristics that potable water must possess.
Then, we will conclude by understanding the differences between pure water and potable water.
What is Potable Water?
Potable water is water which is purified to make it safe for human consumption. Another name for potable water is drinking water.
Remember that potable water is not the same as pure water and hence it is not completely devoid of all impurities, but it is ensured that the concentration of said impurities is low enough so that it won't affect public health. Potable water actually should contain some minerals which are important for our health. Such nutrients and minerals should be present in water so that we don’t suffer from deficiency disorders. Hence, these micronutrients are deliberately added to the water supplies.
For example, zinc is an essential micronutrient that helps in preventing cell damage and maintains a normal metabolism of the human body.
Potable Water Sources
The most common sources of potable water in many countries (including the UK) are:
Rainwater gets accumulated in water bodies like rivers, lakes and reservoirs. These water bodies have exposed surfaces, i.e. they have surface water. The water that seeps into the ground, passing through beds of rocks inside the ground is called groundwater. Groundwater is purer and cleaner than surface water as the surface water is often contaminated with impurities because of exposure.
Fig. 2. Depending on the conditions of the surrounding habitats, you might think that river water looks pretty healthy to drink. However, regardless of its colour and odour, the water of a river carries microorganisms present in the animals that live in or around it.
The surface water or groundwater is then treated in water treatment plants. The treatment of water to make it potable has several phases:
- The water is passed through filters to filter out any visible debris/suspended/insoluble impurities.
- The filtered water is passed through a bed of sand and gravel to filter out the invisible contaminants.
- This water is now sterilized by treating it with chlorine, ozone or UV light. This sterilization process kills the disease-causing microbes present in the water.
Additionally, in some countries where fresh surface water is scarce, seawater is desalinated to remove salts producing potable water.
Fig. 3. Drinking seawater will accomplish the opposite of hydration. The amount of salt present in seawater will dehydrate you.
In countries where surface water is scarce, a water treatment technique called reverse osmosis (RO) is employed. Reverse osmosis uses a semipermeable membrane which filters out the impurities and salt, giving out water that is fit for drinking.
Fig. 4. Reverse Osmosis, Image by Tirtamakmur, CC BY-SA 4.0, via Wikimedia Commons[1] Characteristics of Potable Water
For water to be potable, i.e. suitable for human consumption, it should possess the following characteristics:
The water should be colourless and transparent, not cloudy
The water should be odourless - a mild level of chlorine odour is fine
There should be only low levels of suspended/insoluble solid impurities
Potable water should have minerals, micronutrients and salts
Potable water should be devoid of microbes like Escherichia coli. This is an absolute must because microbes are harmful and might cause some dangerous diseases. So, potable water shouldn’t contain any microbes.
Potable Water Standards
For water to be termed as ‘potable’, it should follow certain standards and guidelines given by the government of that particular country. Governments provide some specifications on how much of a certain substance is acceptable to be present in potable water.
In the UK, these values are often referred to as Prescribed Concentrations and Values (PCV). For example, according to the UK government, the acceptable amount of Fluoride/PCV in potable water is 1.5mg/L.[2] Similarly, the PCV for Enterococci and E. Coli (microbes) is 0 number/ 100mL- meaning the potable water should be completely devoid of microbes.[2]
The pH value of potable water should be between 6.5-9.5, neither extremely acidic nor alkaline.
Differences Between Potable Water and Pure Water
As we discussed in the previous sections, potable water is not pure water, not devoid of impurities. Then, what is pure water? How is it obtained? What are the applications of pure water? We will discuss all these points by comparing pure water with potable water.
Potable water | Pure Water |
Water that is filtered and sterilised to make it safe to drink is potable water. Potable water is fit for human consumption. | Pure water is water that is processed to remove all impurities. It is not ideal for drinking. |
| Potable water is also known as drinking water. | An example of pure water is distilled water, typically used in laboratories. |
It contains some minerals and nutrients that are important for the healthy metabolism of the body, not simply H2O. | Pure water has nothing but H2O. No minerals and nutrients. Frequent consumption will lead to deficiency disorders. |
Potable water can be used for cooking, drinking, and manufacturing beverages. | Pure water is used in: |
Surface water treated with chlorine or ozone or subjected to UV treatments will produce potable water. | Pure water is a result of an evaporation-condensation process called distillation. |
A good conductor of electricity because of dispersed charged ions (Na+, H+, OH-, Ca2+, Cl-). | A very poor conductor of electricity because of very few dispersed ions (the only dispersed ions are H+ and OH-). Most of the distilled water exists as molecules (H2O). |
Table 1. Comparison between potable water and pure water.
Potable Water Examples
Any water that is safe to drink is an example of potable water, but let's list some common examples:
Pipe-borne water from your domestic pipelines.
Water in wells that are protected to avoid contamination.
Collected rainwater.
Protected spring water (this form of potable water comes from groundwater).
Packaged mineral water (but the quality of the plastic used to pack it matters: it might be harmful if good quality plastic is not used).
Fig. 5. To know if the water from a fountain is potable, you should always look for signs surrounding it that will state if it's fit for drinking or not.
Potable Water - Key takeaways
Water which is purified to make it safe for human consumption is called potable water.
Potable water has some minerals that are important for a healthy human metabolism.
The most common sources of potable water are surface water, groundwater and harvested rainwater. These sources are subjected to filtration and chemical treatment to remove microbes and harmful contaminants.
Characteristics of potable water- odourless, colourless, transparent with suspended minerals, but devoid of microbes.
Examples of potable water include- pipe-borne water, water from protected wells, protected spring water and packaged drinking water.
The standards potable water must have, include- pH must be between 6.5-9.5, should not have microbes and minerals must be present at acceptable levels according to the specifications given by the government (Prescribed Concentrations and Values-PCV).
Pure water and potable water are not the same. Pure water is not fit for human consumption as it is devoid of any minerals.
References
- https://commons.wikimedia.org/wiki/File:Reverse_osmosis.png
- https://www.legislation.gov.uk/uksi/2016/614/schedule/1/made
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