Finally, a larger population means greater contamination of rivers, lakes, and streams, and this reduces our supply even more. It has taken plants and animals centuries to adapt to these harsh conditions, but we don't have nearly that much time. This happens in countries where there is plenty of water, but probably not where water is already scarce. This is certainly true, some people think clean, fresh water is limitless. We can't survive without fresh water.
Fresh water contains no salt, no contamination, and is drinkable.
The streams and rivers could be evaporating because the weather is getting warmer. The bigger the population the more water they need to use. They use the water for drinking, cooking, washing, etc. People and factories pollute the water we need to drink, so there is less fresh water. We think that there are several causes.