We propose and investigate a simple model of water, defined on a tetrahedral Husimi lattice. The peculiar nature of the lattice is meant to account for the formation of a random hydrogen bond network with locally tetrahedral coordination. The model turns out to be consistent with most anomalous properties observed in liquid and supercooled-liquid water. Furthermore, at low temperature we observe two glassy phases with different densities, which can apparently coexist at a first-order transition. The complex free-energy landscape characterizing such phases is pointed out by the so-called cavity method, at the level of 1-step replica symmetry breaking. We are led to identify these phases with the low- and high-density amorphous ices observed experimentally.