The Darcy-Weisbach, Hazen-Williams, and Colebrook-White equations are three commonly used equations for calculating pipe pressure drop. The Darcy-Weisbach equation is the most general and accurate equation, but it requires knowledge of the friction factor, which can be difficult to determine. The Hazen-Williams equation is a simplified equation that is widely used for water and wastewater applications, but it is less accurate than the Darcy-Weisbach equation. The Colebrook-White equation is an implicit equation that is used for turbulent flow and requires iteration to solve. Each equation has its own strengths and limitations, and the choice of equation depends on the specific application and available data.