Is silver bearing lead-free solder sufficient/safe enough for water heater plumbing?
Silver Bearing Lead-Free is fine to use. Make sure you clean all fittings and use flux. If installing a new tank, make sure to solder the brass tank connectors to 12" pieces of copper first. Then tighten the tank connectors onto the inlet and outlet using teflon tape. Failing  to do this may cause the dip tube inside of the tank to melt.