A process for alkylation of an alkylatable aromatic compound to produce a monoalkylated aromatic compound, comprising the steps of (a) contacting at least one the alkylatable aromatic compound and at least one the alkylating agent with at least one molecular sieve catalyst under suitable alkylation or transalkylation conditions in at least one reaction zone, to produce at least one effluent which comprises the monoalkylated aromatic compound, wherein the suitable alkylation or transalkylation conditions comprise a water content being in a range from about 1 wppm to about 10 wt. % based on the combined weight of the alkylatable aromatic compound and the alkylating agent; and (b) maintaining the water content in the reaction zone; wherein the cycle length of the molecular sieve catalyst operated inside the range of the water content is greater than the cycle length of the molecular sieve catalyst operated outside the range of the water content.