What limits the lead content of solder and flux used on joints in a potable water system?
- ASolder may contain up to 2 percent lead where the water supply is treated to control leaching.
Water treatment is not an exemption. The limit is a product requirement on the solder itself, and corrosion control programs reduce leaching from existing lead but never authorize installing more of it.
- BLead content is unrestricted on lines smaller than 1 inch, because the wetted surface inside small tubing is too little to matter.
No pipe size threshold exists. Small lines are the ones feeding drinking water fixtures directly, so a size exemption would put lead closest to the point of use.
- CLead is permitted in flux but prohibited in the solder itself, since flux burns off during heating and never contacts the water.
Flux is covered along with solder. Residual flux stays inside the joint and contacts potable water for the life of the system, which is why limiting only the solder would leave the lead source in place.
- Solder and flux used on potable water piping must be lead free, containing not more than 0.2 percent lead
Why D is correct
The code requires solder and flux used on potable water piping to be lead free, defined as containing not more than 0.2 percent lead. A parallel requirement caps the weighted average lead content of the wetted surfaces of pipes, fittings, and fixtures at one quarter of one percent. Both limits are federal in origin and are enforced through product listing and marking.
What this question is testing
This tests knowledge of the lead-free requirement for potable water joints and the fact that flux is regulated alongside solder, plus awareness that a separate wetted-surface limit applies to the pipe and fittings themselves.
On the job
Lead solder is still on shelves for non-potable uses and looks identical to lead-free on the spool. Keep a single lead-free spool in the potable water bag and keep anything else out of the truck. Inspectors do check the spool and the flux can on a repipe. If you inherit a system with lead-solder joints, flushing advice and eventual replacement are the honest answers, not a claim that old joints are harmless.
Memory technique
Lead free means two tenths of a percent, and flux counts too.
Exam tip
Two lead numbers live near each other: solder and flux at two tenths of a percent, wetted surfaces at a quarter percent.
Where to look it up
Chapter 6, the joint provisions for copper and copper alloy tube and the lead content requirements that accompany them. The lead limits are federal and apply in UPC states equally, but the section numbers and wording differ, so use the code your state adopted.