Water towers are as a rule completely free-standing structures. Guying such objects is not preferred as when affected by wind loads the guys have to stand high forces and waves in the tank can occur which can result in dangerous oscillations of the structure. However there are a few one, which are listed on
http://en.wikipedia.org/wiki/Additionally_guyed_tower . But none of them is so tall as that of Ostrowiec Świętokrzyski (
http://www.wieze.republika.pl/Ostrow...krzyski_2.htm), which is 70 metres tall and has a reservoir with 200 m3.
Interestingly the tower seems to be over 40 years old. Do you know further guyed water towers?