I start losing water as soon as the bog plants start to grow, as soon as it is hot/warm and the wind blows. The bog has a huge surface area.
I used to worry, now just check the few places I know can give me a issue (water outlets from the the other ponds) and if they are ok I don't worry. Once I turn the stream on I lose more, the small stream ponds sit during the day losing water and refilled when I run the pump. They lose water due to plants using it up and evaporation.
I start with around 15 minutes of water, mid summer I am up to around 1/2 to 1 hour of water added every day. All auto fed via a irrigation system.
The deer have caused a few issues, on the down slope side of the small ponds, a wall and dirt built up to hold that side. They have walked on the edge, knocking down rocks and the liner and boy does that water run out fast! I have reinforced it again, see if it works this time.