A small amount of water loss can sometimes happen during the hotter times of the year. On a hot day a pond can lose up to 1 1/2” of water from normal evaporation and splash-off. Depending on how much rock boulders and gravel are used, can cause a decent amount of evaporation alone. The temperature of the air can determine the amount of evaporation as well. You should be watching to make sure the water doesn’t drop past a certain level, this can cause a problem to the pump and accessories. If the feature loses water fast when it is on or drops when it is off then call to have someone come and take a look.