The three stages of wastewater treatment are known as primary, secondary and tertiary. Each stage purifies water to a higher level.

Water that is safe for drinking is called potable water. The treatment piece of this process is called the water-treatment process. The water-treatment process involves four steps, in this order: coagulation, sedimentation, filtration, and disinfection.

The treatment process for drinking water varies according to the type and quality of the raw water. Common treatment methods include aeration, flocculation, sedimentation, filtration, and disinfection to ensure water is of a safe quality for consumption.

5.2 Stages in large-scale water treatment

• 1 Screening.
• 2 Aeration.
• 3 Coagulation and flocculation.
• 4 Sedimentation.
• 5 Filtration.
• 6 Chlorination.
• 7 Supplementary treatment.

Viruses are the smallest waterborne microbes (20 to about 100 nanometers in size) and the most difficult to remove by filtration and other size exclusion methods. Bacteria are somewhat larger than viruses (about 0.5 to 3 micrometers) but too small to be readily removed by plain sedimentation or settling.

Tiny amounts of pharmaceuticals — including antibiotics, hormones, mood stabilizers, and other drugs — are in our drinking water supplies, according to a media report. In an investigation by the Associated Press, drinking water supplies in 24 major metropolitan areas were found to include drugs.

Once the floc has settled to the bottom of the water supply, the clear water on top will pass through filters of varying compositions (sand, gravel, and charcoal) and pore sizes, in order to remove dissolved particles, such as dust, parasites, bacteria, viruses, and chemicals.

In some parts of the world, the wastewater that flows down the drain – yes, including toilet flushes – is now being filtered and treated until it’s as pure as spring water, if not more so. It might not sound appealing, but recycled water is safe and tastes like any other drinking water, bottled or tap.

Your bathroom tap water is perfectly fine to brush your teeth and to wash up. As long as you’re not swallowing the water, you’re unlikely to get lead poisoning.

Bill Gates has drunk a glass of water made from human faeces, to showcase technology he said could provide clean water in the developing world. In a video posted on his blog, Mr Gates watched as the human waste was fed into the processor, before drinking the end product from a glass.

Frequent bowel movements is a condition in which a person defecates more often than usual. There are many possible causes, including eating spoiled food, bacterial infection and side effects of a medication. Treatment is usually with an over-the-counter medicine.