Subject: why use H2O in calculating electrolytic cells and not electrochem cells?

When calculating the emf (voltage) needed to be overcome for reaction to occur 
in  an electrolytic cell in aqueous solution we read in books that we also 
consider the half equations of H2O at anode and cathode as it is aqueous 
(makes sense right). Ok.. now, when calculating the voltage generated in an 
electrochemical cell with aqueous solution we dont consider water at the 
electrodes as a possible half reactions or do we? In the texts i have i have 
not seen them consider the half equations of water in an elctrochemical cell. 
why is this?Is it simply not likely that water will be reaction at 
anode/cathode so we dont check the values? Kind regards chris

Re: why use H2O in calculating electrolytic cells and not electrochem cells?