  A lattice model for binary mixture of lipids and water is introduced and
investigated. The orientational degrees of freedom of the amphiphilic molecules
are taken into account in the same way as in the model for oil-water-surfactant
mixtures introduced earlier by Johan H\o ye and co-authors. The ground state of
the model is discussed in detail, and the mean-field stability analysis of the
disordered phase is performed. The model is compared to the recently introduced
lattice model for colloidal self-assembly.
