A method and an apparatus raise samples of liquid such as water from a low level to a higher level, for example for obtaining a sample of groundwater from a borehole. The apparatus comprises a pair of tubes (14 and 16) extending alongside each other, which are introduced into the borehole, linked by a connector (20) at their lower end, a valve (22) communicating between the inside and outside of one of the tubes (16) near its lower end, and a pig (46) insertable into the tube (16). By adjusting the pressure in each tube at their upper end, the pig (46) can be moved from one end to the other of the apparatus (10) and used to transfer samples of water.