Video Transcript
Potable water must be sterilised before it can be drunk. Which of the following is not a common treatment agent in the production of potable water? A) Ultraviolet light. B) Calcium carbonate. C) Chlorine. D) Ozone.
Potable water is another name for drinking water. All the major water sources, seawater, wastewater, and fresh water, contain contaminants like harmful microorganisms, particles, debris, and salt. All these contaminants need to be removed or minimised in the purification process before we make drinkable water.
For this question, we’re looking at the sterilisation step. So we’ll be looking at our four options to see whether they’re effective at sterilisation or not. Let’s start with ultraviolet light. UV light is high energy and is not visible to the human eye. UV light, in the same way it damages skin and causes sunburn, breaks down microorganisms. For this reason, it is a common means of sterilising water and is therefore not a correct answer.
What about calcium carbonate? Calcium carbonate has the formula CaCO₃. And it’s the main constituent of limestone. It is basic in that it reacts with acids. But it’s not antimicrobial. In fact, calcium carbonate is a big contributor to the production of hard water. Groundwater filtering through fishes in limestone pick up calcium ions which later have to be removed. So calcium carbonate is not a common treatment agent used in the production of potable water.
However, I will look at the other options just to make sure we’ve got the correct answer. Chlorine, a gas, can be dissolved in water. Once in water, it reacts to form hydrochloric acid and hypochlorous acid. As well as obviously being acidic, hypochlorous acid is an oxidising agent. This makes chlorine gas a strong antimicrobial agent and is widely used in the water purification industry to disinfect water. This is therefore not a correct answer.
Finally, we come to ozone. Ozone has the formula O₃. It’s a very reactive oxidiser. In fact, it’s a stronger and faster oxidiser than chlorine. It too is widely used as a treatment agent in the production of potable water. Therefore, it too is not a correct answer. So of the four options given, the only one not a common treatment agent in the production of potable water is calcium carbonate.
