a standard spark plug should last 10-20K KM...those better/performance type should last 30-50KM....
Spark plug is wear and tear part...
Also life span of spark plug depend on your engine condition...if your engine makan engine oil / wrong tuning then your spark plug will wear out faster.
Wanna ask, based on the picture, which water line will be the inlet for water into turbo? and how about the oil line also? is the one showing in the picture is the inlet for oil? or the one at the bottom?