Water loss in your water garden is normal if it is little - Disappearance by the inches is a considerable ambiguity to solve. The prior thing is to get the difference and then solve the problem. Look for evaporation clues during the heat of the summer time; you can expect some all-natural water loss.
Evaporation, up to an inch of water will naturally disappear. If you have a long stream bed with a lot of surface area or a large pond with few floating plant, even more water could transform from liquid to vapor. For a pond to lose ½" 3/4" of water per day is not terribly alarming condition.
The amount of water evaporating will depend on
If this is not the issue it means that your pond is having a leak. The automatic fill is always in service; pond owner may live without noticing a small leak. Leaks are a relatively easy find in flexible liner ponds. Inspect the entire pond looking for wet areas outside of the pond. Continuing the investigation, go around the entire perimeter of the pond and look for a leak where the common areas causing a leak.
With extra liner available, a fix can easily be made by pulling up the excess and bringing in some fill soil. Eliminated the relatively simple leaks, like wind-blown water and edge settling. Look thoroughly at all possible leak points in a flexible lined pond, and talk about ways to avoid them. Installing pond liner can be the solution which can last long and not let the problem occur again. As it is like shield to your pond and keeps water in it. It actually minimizes the maintenance work and makes you free from all the tension of Pond leaks.