Cut the butter into small cubes.
Preheat the oven to 400 degrees.
In a nonreactive medium saucepan over low heat, combine the dates, granulated sugar, and water. Cook, stirring constantly, until thickened, about 15 minutes.
In a large bowl or bowl of a mixer, place the brown sugar, flour, baking soda, salt, and oats. Mix on low speed until combined.
With the mixer is running, add the butter, 1 piece or 2 at a time. Mix until it's crumb like, with some lumps of butter no larger than a pea.
Using your hands, press and flatten half of the crumb mixture into a greased 9x13 inch pan.
Spread the cooled filling over the crust.
Cover it with the remaining crumb mixture, patting lightly.
Bake until lightly browned, 25 to 35 minutes.
Cool slightly and cut into bars while still in the pan.
Gently remove the cut bars from the pan.
Serve warm or at room temperature.