The weighted average lead content of a pipe, pipe fitting, plumbing fitting, or fixture shall be calculated by using the following formula: For each wetted component, the percentage of lead is multiplied by the ratio of the wetted surface area of that component to the total wetted surface area of the entire product to arrive at the weighted percentage of lead of the component. The weighted percentage of lead of each wetted component is added together, and the sum of these weighted percentages constitutes the weighted average lead content of the product. The lead content of the material used to produce wetted components is used to determine compliance with paragraph (2) of this subdivision. For lead content of materials that are provided as a range, the maximum content of the range must be used for calculating the weighted average lead content.
N.Y. Comp. Codes R. & Regs. Tit. 10 §§ 5-1.22