A fluid reservoir for retaining a particular fluid against an environmental force is disclosed. The fluid reservoir includes a three dimensional porous body that has a plurality of reservoir capillaries formed therein and has a transport volume and effective capillarity in the force direction for the particular fluid when the porous body is oriented in a predetermined orientation. The fluid reservoir also includes at least one lateral indentation in a surface of the porous body. Each of the at least one lateral indentation defines opposing reservoir surfaces each having a lateral surface component orthogonal to the force direction. The at least one lateral indentation is configured so that at least a majority of the reservoir capillaries have a force-aligned length component that is less than the effective capillarity for the particular fluid.