A microelectronic module includes a substrate having a plurality of mounted electronic components. The components are selected from bare die, chiplets, stacked devices, low-profile packaged devices, optical and electro-optical devices, and surface mount devices. A water-impermeable coating surrounds the microelectronic module except for an opening at the top for making input/output connections. A water-cooled server includes a plurality of the microelectronic modules disposed in a tank with cooling water flowing around the modules.