Abstract: Provided is an apparatus for inducing and/or controlling flow of a fluid within a microchannel in a microfluidic device. The apparatus includes a fluid reservoir configured for holding a volume of fluid to be transported through said microfluidic channel and also configured for fluid connection to an inlet of said microfluidic channel. The apparatus also includes an evaporation reservoir configured for fluid connection to an outlet of said microfluidic channel. The evaporation reservoir includes at least one wetting, wicking or hydrophilic structure positioned at least partly within the reservoir. The wetting, wicking, or hydrophilic structure is capable of absorbing or conducting a fluid present in the microfluidic channel via wicking action or capillary force and maintaining a substantially constant volume of fluid in the evaporation reservoir.