A liquid delivery apparatus for the intrathecal delivery of one or more medications to a patient is disclosed. The liquid delivery apparatus generally includes a liquid reservoir, a liquid metering unit fluidly connected to the liquid reservoir, and a catheter delivery tube fluidly connected to the liquid metering unit. Preferably, the liquid delivery apparatus includes two or more liquid reservoirs. In various embodiments, the liquid reservoir includes a deformable balloon and a compressive sleeve spring as a pressure source, the liquid metering unit is a piezoelectrically actuated microvalve, and/or diagnostic sensors are included in the apparatus. The disclosed apparatus are compact, volume-efficient, energy-efficient, capable of delivering accurate fluid volumes, and address problems associated with multi-medication therapies. Methods of operating the liquid delivery apparatus are also disclosed.