Paperwork the law already asks for
Plumbing record keeping requirements: what the rules make plumbers keep
Updated
Some of a plumbing firm's deepest files exist because a rule required them: lead-safe work records, notices to the water company and certificates for notifiable work.
Plumbing paperwork under US federal rules
Lead-safe renovation records
40 CFR 745.86 says: "Firms performing renovations must retain and, if requested, make available to EPA all records necessary to demonstrate compliance with this subpart for a period of 3 years following completion of the renovation." Cutting into painted walls in older homes to run new pipe can bring a plumbing job under it.
Source: 40 CFR 745.86, renovation recordkeeping
Lead service line inventories sit with the water system
40 CFR 141.84 says: "All water systems must develop an updated initial inventory, known as the “baseline inventory”." The inventory is the water system's, not the plumber's, even where a plumber found the line.
Plumbing paperwork under GB regulations
Notice to the water undertaker
Regulation 5 of the Water Supply (Water Fittings) Regulations 1999 says a person who proposes to install a fitting for listed work "shall give notice to the water undertaker that he proposes to begin work".
Source: Water Supply (Water Fittings) Regulations 1999, regulation 5
Certificates for notifiable work
Regulation 20 of the Building Regulations 2010 has the person carrying out the work act "not more than 30 days after the completion of the work", giving the occupier a copy of the certificate.
Source: Building Regulations 2010, regulation 20
Gas appliance checks
Regulation 36 of the Gas Safety (Installation and Use) Regulations 1998 keeps the record of a landlord's appliance check until there have been two further checks of that appliance or flue.
Source: Gas Safety (Installation and Use) Regulations 1998, regulation 36, for plumbing and heating firms
Kept records and a licence
A licence never takes away a record a rule says the firm must keep: the firm keeps the original and licenses a cleaned copy.