Determine the SFUs for each fixture: Start by identifying the supply fixture units for each plumbing fixture in your system. SFUs are typically provided by plumbing codes or industry standards and represent the demand or flow rate of a specific fixture base on International Plumbing Code(IPC)

Calculate the total SFUs: Add up the SFUs for all the fixtures that will be connected to the water supply system. This will give you the total demand for water in your system.

Consult plumbing code or standards: Check your local plumbing code or industry standards to determine the required flow rate for the water supply. This information is usually provided in gallons per minute (GPM) or liters per second (L/s).

Convert SFUs to flow rate: Using the SFUs and the required flow rate, you can convert the SFUs into an actual flow rate value. Multiply the total SFUs by the conversion factor specified in the plumbing code or standards to obtain the required flow rate.

Size the water supply system: Once you have the required flow rate, you can select the appropriate pipe size and design the water supply system accordingly. Pipe sizing charts and hydraulic calculations can help determine the appropriate pipe diameter and pressure requirements to meet the desired flow rate.

It's important to note that specific plumbing codes and standards may vary depending on your location, so consulting the applicable regulations is essential for accurate water supply design. Additionally, it is recommended to involve a licensed plumber or a professional engineer experienced in plumbing system design to ensure compliance with local regulations and to account for other factors such as pressure losses and building-specific requirements.