In a 3 qt. heavy bottom saucepan over medium high heat bring sugar, corn syrup, salt and water to a boil, Stirring occasionally.
When the mixture reaches 300 degrees on a candy thermometer, remove from stove.
Stir in butter and peanuts.
Stir in the baking soda, be careful it may bubble up. But will become more creamy in texture.
Pour into a rolled edged 1/2 baking sheet. My sheets have a slightly non-stick coating, so I don't butter the sheet, if you pan is not nonstick very lightly butter it so the candy doesn't stick.
Spread mixture evenly over pan, and allow to cool completely.