Using too much water or throwing rubbish into our rivers are clear ways that humans can put our water supply in danger, but we also affect our water supply in less obvious ways. You may wonder how paving(铺砌) a road can lead to less useable fresh water. A major part of the  water we use every day is groundwater. Groundwater does not come from lakes or rivers.It comes from underground. The more roads and parking lots we pave, the less water can flow into the ground to become groundwater.

    Human activity is not responsible for all water shortages. Drier climates are of course more likely to have droughts than areas with more rainfall，but in any case, good management can help to make sure there is enough water to meet our basic needs.

    Thinking about the way we use water every day can make a big difference, too. In the United States, a family of four can use 1.5 tons of water a day! This shows how much we depend on water to live，but there's a lot we can do to lower the number.

You can take steps to save water in your home.To start with, use the same glass for your drinking water all day. Wash it only once a day. Run your dishwasher only when it is full. Help your parents fix any leaks in your home. You can even help to keep our water supply clean by recycling batteries instead of throwing them away.