Is it necessary to buy this kind of bottle to let baby drink water? Baby Is 6 months old~

Firstly, how old is your baby? For the first 6 months of baby's life, water is not necessary as baby will get all the hydration he or she needs from breastmilk and formula. If baby is old enough to drink water, the bottle you suggested looks good, in my opinion. If baby is older, might I suggest a sippy cup?