bettas are adaptable; pretty unparticular about water parameters like pH, hardness, etc. i have some bettas in peat-enriched conditions, and others in straight dechlorinated 7.8 tapwater.
their natural habitat contains soft, acidic water, which is definitely preferred if possible.
other than that... just make sure to keep up with water changes, because if it's let go too long, they get very susceptible to fin rot.