I have not seen clear solder before?
Looks like epoxy cement:shock:
They use it to glue golf clubs too:mrgreen:
Cheers
It looks like flux,a flowing agent brushed on before soldering is done.
Did it feel soft and greasy?
From the photo it looks like the soldering was not done.
Was this a new constuction Inspection or a new water heater install?Was the water on?
If it’s left unsoldered it WILL leak and worse blow apart.
I would go back and check again.
That’s what it looks like to me too…did you touch it Brian?
“Similar in appearance to epoxy adhesive intended for this use”:
http://superglue.supergluecorp.com/copperbond.html
http://supergluepds.com/pdsdocs.aspx?partno=80582
Of course, you can’t determine this for certain, that (unless you check) it’s acceptable to the local AHJ, or that that it was installed “per manufacturer’s instructions” …
It was not flux guys. 
Copper glue, well I’ll be. Thank you Michael