According to the National Center for Atmospheric Research, a typical thunderstorm cloud holds around 275 million gallons of water. If you stand and watch Niagara Falls for six minutes, that’s how much water you’ll see.
But how much of that water actually falls out of the cloud and on to the ground, when it rains? That depends on two things: how big an area we’re talking about and how heavy a rainstorm it is.
Let’s imagine a typical suburban yard, a quarter of an acre in size, and a storm that releases ¼ of an inch of water. In that case, the yard receives almost 1,700 gallons of water from that storm alone.
What about a town of, say, 8,000 people, two square miles in size? From our ¼ inch rainstorm, that little town would receive over 8 ½ million gallons of water.
Of course, a storm that delivers ¼ inch of water is a pretty good storm, but there are plenty of storms that are stronger than that, too.