Homeostasis is a process which by certain organism has a steady balance of certain attributes that maintain an equilibrium. Of course, the response to stimulus is a way of getting to homeostasis but this certain part of life, maintaining homeostasis, is exactly that, maintaining it. Basically what I mean is response to stimulus get the balance, homeostasis has to keep the balance. This is very important.
This balance can be associated with frogs and flies. When a new group of flies are born the frogs are greatly outnumbered. However, their response to a change, stimulus, kicks in. They start filling their stomachs and finally make a balance between the fly population and the frog population. The number of flies are not the same as the number of frogs but there is a balance. Now, all the frogs have to do is keep that balance.
However, with more food the frog population will grow and be able to support more frogs. Then, the frog population will outnumber the flies and unless the frogs can be maintained by birds or other creatures, the flies will be taking care of, forever!
This is homeostasis. There has to be a balance. The fly population may grow then decrease as frogs increase and then increase as frogs decrease and then start all over again. Only when a third, fourth or how many more (birds, etc) are entered can the outcome come to balance. This is a requirement for life but non-life can mimic it.
Let’s use our water analogy again. The rock falls on the river, dams it up and the water has to respond. It overflows the rock or goes around. Currently the rock is prevailing. The water, however, with the right amount of erosion will eventually degrade that rock until it is even. It may be slow but it is responding to stimulus and trying to maintain homeostasis.