Melt butter in a large or medium pot over medium heat. Add flour and cook for one minute.
Add about 3/4th cup of milk and mix into butter mixture - it will become a slurry pretty quickly. Add remaining milk and mix so the slurry mixes in. Then add water and seasonings (garlic powder, onion powder and mustard powder)
Add macaroni and mix. Stir occasionally as it comes to heat. When you see wisps of steam as you stir, lower the heat down to medium low. Stir regularly as it cooks for 9-10 mins. It also bubbles gently, or until the sauce thickens and the macaroni is just cooked - tender but still firm. It should be saucy at this stage and thinner as well.
Take it off the heat and stir in the cheese quickly. Adjust salt and pepper to taste. Also in this step, the sauce thickens and reduces considerably. I like to use mozzarella and cheddar because I feel this combination tastes better. Serve immediately.
