Adding water flosser to your dental hygiene is a very good option. You can use daily before sleeping as it will help maintain your dental health. There are different settings and modes on which to use and that you need to ask your dentist. They will be in better position to tell you to use which mode as it depends on your gum health.

You can use it once daily as your night time oral hygiene  maintenance routine...however, only if the causative factors that is plaque and calculus has been removed  professionally by your dentist then using water flosser works.