When you come inside for a cold drink after a frolic at the park or a long bike ride with some friends, you might not give much thought to turning on the kitchen faucet or pushing a button on your refrigerator for a clear, cool thirst quencher. But making sure your H2O is good to go doesn’t happen by magic. Water purification is an essential process that has developed over thousands—yes, thousands!—of years, since ancient times. Without the scientific questions and discoveries that have occurred over all that time and the water treatment processes and plants that exist today, our daily lives would be vastly different and much more challenging.
Have you ever wondered how your house gets running water that is safe for drinking, bathing, and brushing your teeth? Why do your parents tell you not to drink the water from sprinklers and hoses?
H20 Purification 101: Sedimentation, Filtration, and Disinfection
The answers to those questions start at our water sources—freshwater lakes, rivers, wells, and streams. The first step to bring water from natural to drinkable is by separating the solids—dirt, rocks, and other elements—from the liquid, a process called sedimentation. A chemical called a coagulant—usually ammonium sulfate—is added to the water to help make the solids in the water stick together, making them easier to remove. The water is mixed in a basin, and the solids that are sticking together form floc particles, which settle out into a sedimentation basin, leaving cleaner water flowing on top.
Before you can hydrate, there are still some solids, chemicals, and bacteria left, which may make the water look murky and also can make you sick. The next step is to put the water through a sand filter. Water is pumped, usually from bottom to top, through a basin of fine to coarse sand particles, gravel, and charcoal, which further removes solid particles left over from the sedimentation process. After sand filtering, the water will look clear and ready to drink…but wait!
Not so fast—don’t take a sip yet, because bacteria remains in the water that is invisible to the naked eye. The water has to be disinfected, which is done in one of two ways. Chlorine-based chemicals can be added to the water, which kills the bacteria. However, too much chlorine in the water can cause reactions with leftover organic materials, forming byproducts that can be harmful to people and animals. Levels of chlorination are monitored to ensure they stay within safe levels. The other method of disinfection uses UV radiation, which prevents the bacteria from reproducing, making them harmless to ingest. The water is then stored in the huge round towers you may see along roads and highways, and pumped to our homes through underground pipes.
Voila! Go ahead and gulp your clean, fresh water!
Note: Before you lap some water from a hose or your neighbor’s sprinkler, keep in mind that the water used for lawn irrigation, your garden, or your car may not be filtered to the same standards and may not be safe for drinking.
A Global Crisis
Sadly, even today, many countries across the world still do not have access to clean water. There are an estimated 800 million people who struggle to have life’s most basic necessity. Families may have to travel many miles for meager water supplies and often suffer from disease and poverty, and children have a hard time attending school regularly due to the time spent having to find drinkable water. The global water crisis remains a huge concern, even with our knowledge of the water purification process. Many organizations are working hard to solve this problem through education and activism.
Next time you turn on the tap and grab a drink of water, make some observations and think about the process and people that work 24/7 to make your water clean, clear, and taste good. Make sure to keep natural sources of water clean by throwing away trash in the proper places and not polluting. What can we do to make sure everyone in the world has clean water? Our vital water resources must never be taken for granted.
For more about water purification check out our “Clean Water Act” box for a Lesson in Water Filtration. During your ENGINEERING DESIGN CHALLENGE you will investigate crystals, solubility, evaporation, and much, much, more.