From Quora:

It is absolutely legal to live off-grid.

But…

You have to follow the regulations about it.

If you want to disconnect from city water, you have to show that you have a source for treated potable water. You can't just collect runoff from your roof. Why? In Florida, many shingles are treated with poison to inhibit mold and moss growth. If you want to collect rainwater, you have to show that it's drinkable, properly collected, and properly treated.

If you want to disconnect from sewer, you can't do what she did and just spread your piss and fecal matter all over your yard. You have to show that you have a proper composting toilet. Contrary to the hysterics on certain breathless Web sites, Florida not only permits composting toilets, it even maintains a handy list of approved composting toilet manufacturers.

And:

As other answers have said, you are free to “cut the cord” and live without any number of modern conveniences, including Internet, cable TV, or even electricity. It is also totally legal to make alternate arrangements for heating/cooking fuels, water, wastewater and trash. However, those alternate arrangements must be in accordance with applicable federal, state and local laws designed to control environmental damage and preserve public health.