Well, you want to have a good and positive experience. There are definitely areas which I would not consider safe for Gringos to wander around and see how the locals live. I know in my neighborhood, they've taken to intimidating and asking for stuff. "hey gringo, I want your sunglasses." I was on my motorcycle and one came up and asked for my tires. I laughed and said that he couldn't have them. However, the tourists are freaked out enough to hand over whatever. And, it goes rapidly down hill from there. Fear seems invites the predator instinct.
Even places that look inviting are trouble spots. The Malecon is a nice sidewalk that goes past idealic beaches, but it seems to be a constant source of violence and prostitution.
I'd recommend linking up with a taxi driver that can take you around and help keep you safe. I'm sure some people here can recommend somebody. I don't know of anybody that is bilingual.
Water is warm. People swim all the time, but be sure to take a good shower afterward. Sanitation isn't the best and as advertised on Nemo, all pipes lead to the ocean.
And, bottled water only including brushing your teeth.
As mentioned, it's all normal for a 3rd world country, but I'd exercise some caution if you're not use to it. If not, I'd recommend a All inclusive resort and venture out in the daytime with a taxi driver. If you like it, great. If not, you can still enjoy your vacation and time here.