I'm from the u.S. and have drank the water all over P.V. and have eaten all over town and have never gotten sick in the 20 years we've been going to Mexico. You shouldn't worry about this, especially in P.V. I've been told while traveling to other countries, eat yogurt every day for a week or two before you leave and it can help with stomach problems.
I've found P.V. to be very safe. We've never had any problems there. You're in the marina area and it's very safe to walk around there with your children. It's safe in the downtown areas, Yelapa, Bucerias, ect. I'm sure there are unsafe places like any city everywhere, but I don't know where they are or have never come across them.
Please get out and see the sights and all the town has to offer. You are going to have a blast. It's a fantastic place for a family.