Question
In the past, we have shut down our irrigation system for the winter season (NE Florida) and none of the plants/grass have died.  I am looking for backup info to explain to a neighbor who thinks we should water twice a week through the winter.

Answer
I am flattered but I do not think that your neighbor would be moved by my opinion. Your County Extension Service will be able to provide all the information to back up their recommendations for irrigation during the winter in your area. To contact the CES, go to the EDIS website and click on the 'Local Offices' line. Select the county in which you live and their website will appear.
In summary, water promotes plant growth when light and temperature are also conducive. During the winter, light and temperature are not at the best levels for lush growth; indeed, some plants go dormant. Plants should therefore be watered less frequently otherwise their health will suffer.
There is a set of circumstances when it will help to irrigate. If freezing temperatures are expected, some protection can be obtained by watering the ground beforehand if there is a lot of sunshine. The sun warms up the water in the soil and this water will retain the heat after the sun has gone down. This can make the difference between life and death for some plants. Water has the ability to retain heat better than any other substance. That is why at daybreak, the ocean is warmer than the land.