Combine macaroni, milk, water, butter, salt, garlic powder, and Dijon mustard in a large pot over medium-high heat.
Bring to a boil, then immediately reduce heat to medium-low to maintain a steady simmer.
Cook for 10 to 12 minutes, stirring frequently to prevent sticking, until pasta is al dente and liquid has thickened into a creamy coating.
Remove pot from heat once the liquid has reduced by approximately two-thirds.
Add the shredded cheddar, mozzarella, and parmesan cheese in small batches, stirring constantly until fully melted and emulsified.
Fold in the black pepper and cayenne pepper.
Adjust consistency with a splash of warm milk if a thinner sauce is desired and serve immediately.