Grease a cookie sheet and set it aside.
Add the sugar and light corn syrup to a medium to large saucepan and mix. Turn the burner on medium-high heat.
Next, add the chopped pecans, water, and salt and stir to coat.
Place the candy thermometer into the pan and cook until the thermometer reaches 275-degrees, stirring often.
Once the thermometer reaches 275-degrees, remove it from the pan, remove the pan from on top of the burner, and stir in the butter until melted.
Add the baking soda and mix well (it will foam up some).
Quickly pour the pecan brittle onto the prepared cookie sheet and spread it out.
Allow the pecan brittle to cool for at least one hour. (It will smooth out and get shiny as it cools).
Break the pecan brittle into pieces.