The water in Tahiti might taste slightly salty when you drink it but the water in Tahiti is safe to drink.
Many people in Tahiti and those who live in Tahiti drink the tap water safely although you might have to get used to the salty taste.
That also goes for Moorea and Bora Bora as well for the tap water so there's no need to have other water since the Tap water in those places including Tahiti is safe to drink although can taste salty.