Food Coloring is often used to aid in the identification of a water leak. Leaks commonly occur in pools, fountains and ponds and often the simple solution in a residential setting requires a "do it yourself" attitude which will likely require at least a quart of dye. It is best to start the testing with a color that will contrast well with the surroundings of the area that the water is collecting around. For obvious reasons green food coloring would be a poor choice if the water saturation was on grass or other plant matter. Another factor to consider is that it may be necessary to keep the colored water for a period of time after the testing in areas where the high cost of water would prevent immediately draining the entire volume. In this case a blue hue would appear as normal in most pools and fountains. By identifying a potential leak prior to calling in the professionals, you have to opportunity to state the problem area ahead of time and will be better positioned to negotiate a contract consisting of a fixed rate.