Chemical bath deposition is an inexpensive, low temperature, aqueous method for depositing oxide and chalcogenide thin films and nanostructures. However, such process frequently results in deposition yields of less than 5% and excessive waste solvent. Here we report the synthesis of ZnO nanowire arrays using a novel reactor which results in deposition yields of over 80% and reduces the waste solvent volume by a factor of 20. Furthermore our reactor design allows careful study of the thermodynamics and kinetics of ZnO formation. Nanowires are single crystals with strong UV photoluminescence. Dense arrays of well-aligned nanowires with diameters of 60 - 100 nm were grown on substrates pre-seeded with a thin polycrystalline ZnO film. Such nanowire arrays have applications in nanostructured solar cells, gas sensors, and photocatalysis.