Potable Water

What is Potable 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.

Potable Water Sources

The most common sources of potable water in many countries (including the UK) are:

• Surface water.

• Groundwater.

• Harvested/collected rainwater.

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:

1. The water is passed through filters to filter out any visible debris/suspended/insoluble impurities.
2. The filtered water is passed through a bed of sand and gravel to filter out the invisible contaminants.
3. 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.

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.