There should be plenty of fresh water available for 12 billion humans and the rest of the living biosphere. It is about one percent of the total of water on earth. However, we are, with 7 and a quarter billion people reaching the limits of available fresh water. Almost all available fresh water is polluted or contaminated in some way and we either don't want to or cannot live close to abundant supplies. 70% of fresh water is tied up in ice which we humans in our wisdom are doing our best to melt into the seas. See the Greenland ice sheet and the huge lakes of the Canadian Shield in this first picture.
There's no planet B
This is an arial view of the mouth of the Amazon river. Only about five percent of this fresh water source is available for human use. For a good overview of planetary freshwater resources see: http://goo.gl/1nPJx it was published in 2006. Suffice it to say that nine years later the situation is much worse.