# Equilibrium expression for dissolution of carbon dioxide

I was asked to give the equilibrium expression for:

$$\ce{CO2(aq) + H2O(l) <=> H2CO3(aq)}$$

As water is a liquid and a solvent here, it shouldn't be included in the expression, hence I wrote:

$$K_c = \frac{[\ce{H2CO3}]}{[\ce{CO2}]}$$

However, the answer of the question included water in the denominator.

What is the correct answer in this situation?

$$K_c' = K_c[\ce{H2O}]$$