Since the Safe Drinking Water Act Amendments of 1986 the use of lead-containing solders in potable water systems has effectively been banned nationwide. The major impact of the Act has been on solder containing 50% tin and 50% lead (50-50), until then the most widely used solder for drinking water systems.
Lead-base solders have been replaced by tin-antimony and tin-silver solders. The main differences between these solders and 50-50 are that they are stronger and require somewhat higher working temperatures. Many plumbers in the United States have used them in copper plumbing systems for decades
Reasons for the Ban
The basis for the public health concern is the maximum contaminant level (MCL) for lead in drinking water established by the U.S. Environmental Protection Agency (EPA). EPA has set this MCL at 50 parts per billion for drinking water. This is a very tiny amount of contamination by lead - .000005%. The practical result of this extremely low limit is that some drinking waters which are soft, acidic and have low alkalinity can pick up (leach out) this much lead from any solder which is exposed to the water inside the plumbing system. Studies by EPA and others have shown that in the rare instances where conditions are such that lead pick-up occurs, it generally tapers off to a low level quickly after a new plumbing system is put into use, and also that it is almost always associated with long periods of stagnation of the soft, acidic water inside the plumbing system.
The Water Treatment Option
Lead pick-up can be avoided by treating a soft, acidic, low alkalinity water to make it non-aggressive. MCL's are enforceable at the consumer's water faucet. EPA's position is that the water supplier is responsible for the lead content at that point, even though the lead is picked up from the plumbing system within the home or other building. EPA believes that the water supplier should provide water that is non-aggressive with respect to plumbing systems. In some communities (e.g., Seattle, Washington), this obligation has been recognized and public water supplies are treated with lime or soda ash to control pH and alkalinity and insure against lead pick-up in the system.
Solder selection is normally based on three main considerations: ease of use, service conditions and cost.
In the past fifty-fifty tin-lead solder was widely used because it was the most familiar to the plumbing trade and the easiest to use. It provided the installer with the opportunity to solder at low temperature and, because of its wide melting range, it filled capillary spaces easily.
However, alternative solders can be applied with equal success using the same equipment used for 50-50 and without any need for retraining. In fact, those installers who are already familiar with these materials find them as easy to use as 50-50.
These lead-free solders are applied using the same fluxes, heating equipment and joining techniques as for lead-base solders. Because of their compositions, they are more fluid and less sluggish through their melting ranges than 50-50. Within the standard tolerance range for tube and fittings, which normally provides a capillary soldering space of .002 to .006 in., joints can be made with the same ease with the alternative solders as with the familiar, more pasty 50-50 composition. For very large diameter tube, where there is more possibility of capillary spaces being greater than .006 in., brazing may be the best alternative.
One major advantage of the tin-antimony and tin-silver solders is that joints made with them are considerably stronger than joints made with 50-50 tin-lead. This superiority is the main reason that tin-antimony and tin-silver solders have long been specified for high-rise installations, for high-temperature service, for commercial refrigeration and air conditioning hook-ups and for soldered copper fire sprinkler systems. Because soldered joints made with tin-antimony and tin-silver are stronger, plumbing systems installed using them can withstand higher pressures and temperatures than systems made with 50-50 tin-lead solder.
The alternative solders cost somewhat more per pound than 50-50. Offsetting this higher material cost is the fact that 20 to 25% more joints can be made per pound of tin-antimony and tin-silver solders because they are lighter in weight (lower density) than 50-50. While the cost of tin-antimony solders is almost twice that of 50-50, and tin-silver solders are about four times as expensive, it should be appreciated that the average dwelling unit requires only one or two pounds of solder to install its potable water system. The increased cost of the alternative solder is thus completely insignificant in the cost of a home - and the joints made with it are stronger, safer at elevated temperature and assuredly lead-free.