Grease an 8X13 inch cookie sheet with butter. 

In a medium heavy saucepan, mix water, sugar, light corn syrup, and salt and bring it to a boil while on medium heat. 

Stir in the peanuts and vanilla extract. 

Insert a candy thermometer and stir frequently till the temperature reaches 300 degrees F (150 degrees C).

Remove from heat and stir in the butter and baking soda immediately. 

Pour at once into the greased cookie sheet. With forks or a wooden spatula, spread the sticky mixture evenly. Allow the peanut brittle to cool. 

Once the brittle has completely cooled, break into pieces. Enjoy immediately! You can even store in an air-tight container for up to 2 weeks.