Water Cycle: From Cloud to Tap

Dec. 22, 2014

By Kim Dyches

It’s easy to take our drinking water for granted—we turn on our tap and just like that, we have clean water. In fact, Americans drink more than 1 billion glasses of tap water a day! But strict regulations to protect the quality of that drinking water are a relatively recent development. That’s why the Division of Drinking Water (DDW) is celebrating the 40th anniversary of the Safe Drinking Water Act (SDWA) this month. SDWA ensures that water suppliers provide the public with safe, clean drinking water, protect ground water sources from contamination, and test water regularly to make sure it meets health-based drinking water standards.

But let’s step back for a moment. Where does our water come from, and how do we make sure it’s safe to drink?

It all starts with the water cycle, a process that transfers water from the atmosphere down to the earth and back again. Water droplets evaporate from the ground into the atmosphere, cool, and condense to form clouds. As the clouds become saturated, the water falls to the ground as rain or snow. This precipitation nourishes plants, flows into surface waters, collects as snowpack in the mountains, or percolates through the soil to become ground water. The cycle begins again as the heat of the sun causes surface water to evaporate and plants release water vapor into the air. This continuous movement of water from solid to gas to liquid has been going on for millennia.

Precipitation from the water cycle provides us with the surface water or ground water that is the source of our drinking water. While it would be ideal if these water sources were pristine, they are often contaminated by chemicals, microbes, waste products, or even naturally occurring substances.


Prior to the enactment of the SDWA, the safety of drinking water was far from assured. Chlorination of water supplies in the U.S. began in the early 1900s and was a public health triumph, greatly reducing the incidence of typhus and cholera from contaminated water. Still, a 1969 Public Health Service study of public water suppliers in five states found that more than 40 percent of residents were drinking substandard water and up to 8 million Americans were drinking potentially dangerous water. The study found that most systems weren’t regularly testing for chemicals in the water and most couldn’t pass state bacteriological standards.


SDWA changed all that in 1974. The law set national health-based standards for drinking water from public water suppliers, and later added requirements for source water protection and operator training, funding for water system improvements, and public information on drinking water systems. DDW is responsible for implementing these requirements, and our program includes:

So the next time you turn on your tap, remember that DDW is working hard every day to ensure that every precious drop of water we get from the water cycle is treated and protected so you can count on safe drinking water every time you fill your glass.

Want to know more about the water cycle and your drinking water? Your water system is required under SDWA to prepare and distribute an annual Consumer Confidence Report (CCR) to residents. You can contact your local water supplier for a copy of their latest report or check out the EPA locator to see if the report is available online. Visit our web page to learn more about our wide range of programs to protect your drinking water. To learn more about SDWA and how it’s helped us protect our drinking water, visit the EPA Safe Drinking Water site for more information.
Kim Dyches

I am the Field Services Manager for the Division of Drinking Water. I have been in the water industry for 30 years. I am adjunct faculty at Utah Valley University and have taught several courses on subjects relating to water.