Wet string is a
jargon term for a low quality
communications link. It is in theory possible to transmit data between two pieces of communication equipment over
string or
twine, if the string is wet - owing to water's conductive properties. see
http://www.alangm4.clara.net/wetString.htm and
http://www.airborn.com.au/photo1/workshop.html for examples of people actually trying this out.
Drawing on the analogy of audio communication using a piece of taut string between two empty cans, the jargon term wet string is often used to denote a worst case scenario for a communications link between two points in a network. Hence the humourous excuse for the network going down "The string dried out because the sun's been shining too much".