They also prefer distilled water. If you run a dehumidifier, the water it accumulates is perfect. Begonias do well in average indoor winter temperatures and our average outdoor summer temperatures. When it is warm in the summer, they benefit from misting a few times each week. Fertilize once a month during fall and winter.
Excellent drainage is important, so the best soil is a lightweight peat-based potting medium.
They like to be a little pot-bound, so they won't need repotting very often. If you slide them gently out of their container and they seem to be all roots and very little soil, that is when they should be repotted into a slightly larger container. Their large, showy leaves can collect dust that can be gently removed with a soft-brush. Avoid using leafshine. Because their stems and leaves are brittle, an occasional damaged leaf will need to be removed.