Combining a carbon nanotube probe and a highly sensitive dynamic measurement scheme has enabled us to use atomic force microscopy to measure oscillatory forces in water on approaching a surface that has been laterally characterized on a nanometer scale. This opens up the possibility of investigating water layers under a variety of experimental conditions and as a function of precise lateral position on any surface including biological membranes and macromolecules. Among the many and varied roles of water layers are effects on biomolecular adhesion, colloid dispersion, and tribology, which can now be investigated with nanometer lateral resolution and with a wider range of materials than that previously provided by surface forces appartus.