What is the minimum size of water supply pipe for lavatories?

The minimum size of water supply pipe for lavatories is determined by factors such as water flow requirements and pressure considerations. A 3/8 inch pipe size is essential because it provides adequate water flow for typical lavatory fixtures, ensuring that they operate effectively while meeting code requirements. This diameter is sufficient to supply the necessary volume of water for both cold and hot supply lines to lavatories, which typically do not require as large a diameter as other fixtures like toilets or showers.

While smaller diameters might not support the flow needs adequately, opting for a size larger than 3/8 inch may unnecessarily increase costs and resource usage without any significant benefit for most residential lavatory setups. Thus, the choice of 3/8 inch balances performance, efficiency, and compliance with plumbing codes.