Melt the butter. Mix melted butter with water and taco seasoning mix.
Pour half of seasoning over cereal and mix well with hands. Pour remaining seasoning mix over cereal and stir well.
Pour onto a baking sheet and bake in preheated oven for 1 hour; stirring every 15 minutes.
Notes
I found the easiest way to stir it was to have a large bowl on hand, remove the baking sheet from the oven and pour the contents into the bowl, stir, then return to the baking sheet.