Petroleum, a fossil fuel, supplies more energy to the world today than any other source. The United States is the world's leading consumer of petroleum; in 1994, Americans used 7,587,000 barrels of oil per day.
Frequently test for ammonia and nitrite (you want both to measure zero). A pH test is also handy to ensure your goldfish's water is not too alkaline or acidic. This can be purchased at any pet store. Do not modify the fish's water, however, unless it is significantly different from neutral.
This allows the chlorine to evaporate. It also lets the water reach room temperature. Since goldfishes live at room temperature, this ensures that the water you are adding to the tank is the same temperature as the water already in the tank. Finally, the most important thing to know about is the water change.