Skip to content
Know Your Pipes A reference to home pipe and fittings A–ZDid you know
Browse categories

Lead-free solder

Entry in Sizes, codes and marks · Updated · Written by the Know Your Pipes editors from the sources listed under References

Lead-free solder is plumbing solder, and the flux used with it, containing no more than 0.2% lead, the only kind US federal law allows on pipes that carry drinking water.[1] It is used chiefly to make soldered (sweat) joints between copper tube and copper or brass fittings.

1 The federal rule

The Safe Drinking Water Act, as amended in 1986, bars any pipe, fitting, fixture, solder or flux that is not "lead free" from use after June 19, 1986, in public water systems and in building plumbing that supplies water for human consumption.[2] For solder and flux the limit was set at 0.2% lead; pipe and pipe fittings were then allowed up to 8%.[2] Congress's 2011 Reduction of Lead in Drinking Water Act, effective January 4, 2014, lowered the limit for the wetted surfaces of pipes, fittings and fixtures to a weighted average of 0.25%, while the 0.2% limit for solder and flux stayed the same.[2][1]

States enforce the rule through state or local plumbing codes, so the wording an inspector applies comes from the adopted plumbing code.[2] A 1996 amendment added sales rules that took effect two years later: plumbing-supply sellers other than manufacturers may not sell solder or flux that is not lead free, and any such solder put on the market must carry a prominent label saying it is illegal to use in plumbing for drinking water.[2]

2 Alloys

With lead removed, tin becomes the main metal, alloyed with antimony, copper or silver.[3] ASTM B32 covers the alloys; besides 95/5 tin-antimony (Alloy Sb5) it lists lead-free Alloys E and HB, which the Copper Development Association rates as suited to higher pressures than 50-50 tin-lead.[4]

Common lead-free plumbing solders
AlloyMake-upMelting range
95/5About 95% tin, 5% antimony (ASTM B32 Alloy Sb5)452–464°F[5]
97/397% tin, 3% copper440–572°F[3]
Silver-bearingTin with a small share of silver420–460°F[3]

The 95/5 alloy melts over a narrow range, and its maker notes that it needs close-fitting joints because it does not readily bridge wide gaps.[5] That maker lists it as certified to NSF/ANSI 61 Annex G and NSF/ANSI 372.[5] The 97/3 alloy has the widest melting range of the three and, according to one maker, is preferred in some regions, especially the southern United States.[3]

3 Flux and 50-50 solder

Flux removes oxide traces, helps molten solder wet the metal and protects the surfaces from oxidation while they are heated; the Copper Development Association recommends fluxes meeting ASTM B813.[4] It warns that strongly corrosive "self-cleaning" fluxes can leave residue that keeps acting after the joint is made, and excess flux left inside tube is one recognized cause of pinhole leaks.[4]

Solder containing more than 0.2% lead is banned on drinking-water systems; 50-50 tin-lead may still be allowed for some heating, drainage and other non-potable piping in some jurisdictions.[4] Houses plumbed before 1986 can still contain lead solder, and EPA names it, along with brass faucets, as the most common lead source in homes without a lead service line.[6] Supply houses sell solder by alloy and spool size; PlumbingSupplyAndMore's solder category (PlumbingSupplyAndMore has the same owners as this reference) is one example.

See also

  • Lead pipe and lead service linesSoft gray lead water pipe, mostly in service lines; how to recognize it and what EPA's 2024 rule requires of water systems.
  • Copper pipe types K, L and MThe three wall grades of copper water tube under ASTM B88, how to tell them apart and where each is normally used.
  • Soldered (sweat) jointsHow a sweat fitting is soldered to copper tube by capillary action, which solders are lawful for drinking water, and how brazing differs.
  • NSF/ANSI/CAN 372 (lead content)The standard used to certify plumbing products to the federal 0.25% lead-free limit, and how to read its marks.
  • Pinhole leaks in copper pipeSmall leaks in copper water tube caused by pitting corrosion, and the water, flow and workmanship factors linked to them.
  • Nominal pipe size, CTS and IPSWhy pipe sizes are names rather than measurements, and how the CTS and IPS outside-diameter systems differ for the same nominal size.

References

  1. U.S. Environmental Protection Agency, "Use of Lead Free Pipes, Fittings, Fixtures, Solder, and Flux for Drinking Water" (2026) — epa.gov
  2. U.S. Environmental Protection Agency, Office of Water, "Lead-Free Definition Under the Safe Drinking Water Act" (2012) — epa.gov
  3. Oatey, "What Are the Different Types of Solder?" — oatey.com
  4. Copper Development Association, "The Copper Tube Handbook" (2006) — pages.mtu.edu
  5. The Harris Products Group, "Technical Information Sheet: 95-5 Tin & Antimony Lead-Free Solder" — ch-delivery.lincolnelectric.com
  6. U.S. Environmental Protection Agency, "Basic Information about Lead in Drinking Water" — epa.gov