The ultimate goal of nanotechnology is to construct integrated complex nanosystems with various functions. To achieve this goal, one must first establish solid, yet simple, nanounits (or nanoparts) such as nanomotors and nanoflowmeters. In this work, we computationally designed a novel nanoflowmeter based on two carbon nanotubes, with a smaller inner chiral tube as the "rotator" and a larger outer tube as the "stator" (or container), to measure the fluid flow between the two nanotubes. We found that the water nanoflowmeter could be gauged by the unidirectional motion of the chiral nanorotator even under severe thermal fluctuations at the nanoscale. The nanoflowmeter exhibited an excellent correlation between the cumulative net flux of water and the net rotation angle, which served as the underlying mechanism for our nanoflowmeter measurements. We then further optimized the design of the nanoflowmeter by introducing partial charges onto the inner rotator with "screwlike patterns" to enhance the chirality. The concerted motion of the water molecules could then be modulated by these partial charges, which direct the dipole orientation of water molecules and form a tailored configuration of a hydrogen-bond network in nanoconfinement. The present findings from molecular modeling could provide the foundation for a more sophisticated and practical nanoflowmeter. © 2012 American Chemical Society.