Washing your hair twice everyday if needed can be safe and healthy for the hair but you need to use moisturizing shampoo to avoid drying out your hair and removing essential oils from your hair.
When you wash your hair too often you risk washing away the needed oils that are in your hair which can cause damage to your hair overtime.
Only wash your hair twice per day if you really need too and do so with the proper shampoo but if you don't have to wash your hair everyday then I would advise against it to avoid damaging your hair.
Usually every other day is good enough for washing your hair.