Dave Liquorice wrote:

"Lead free solder" should be used on potable water supplies. Gas,
heating etc I don't think is specified.

I looked on the BES website to see what solders they sell

http://www.bes.co.uk/products/212.asp

the lead free solders required for potable water are to

BS 219 grade 99C
BS EN 29453 alloy #23
BS EN ISO 9453:2006 alloy #401

depending how historic or up to date you want to be

The BSOL site requires silverlight which I normally have disabled, I did
enable it to try to view the ISO version, but silverlight crashed, so I
looked at the Johnson Matthey product spec instead

http://www.jm-metaljoining.com/pdfs-products/Copper-Tin%20solders.pdf

The everyday lead-free solder is 99% tin, 1% copper.