Ethene does not react with water as such. Water being little polar, is not in a position to provide `H^(+)` ion for initial electrophilic attack on ethene. The reaction is carried in the presence of `H_(2)SO_(4)`. The acid provides proton `(H^(+))` for the initial electrophilic attack.
In the second step, `H_(2)O` attracks the carbocation in preference to `HSO_(4)^(-)` ion as a nucleophile
