What is the nominal size of pipe most commonly used for domestic water lines?

The nominal size of pipe most commonly used for domestic water lines is 3/4 inch. This size is widely accepted in residential plumbing due to its capacity for delivering sufficient water flow for typical household needs without being excessively large, which could lead to issues such as increased costs and difficulty in installation.

3/4 inch pipes strike a balance between maintaining adequate pressure and flow rates while being manageable for installation in standard plumbing layouts. This size is particularly effective for branch lines that serve fixtures such as faucets, toilets, and showers, making it a standard choice among plumbers and contractors.

Larger sizes, like 1 inch or more, are generally reserved for main lines or specific applications where higher water volumes are necessary, but using such sizes for typical domestic purposes might not be efficient or practical. Therefore, the preference for 3/4 inch pipe in most domestic settings reflects an industry standard that ensures both functionality and cost-effectiveness.