A connection system (100) comprises a connector (101) and a pipe (102). The pipe (101) is made from a hydrophilic membrane capable of pervaporating brackish water or such like as substantially pure water, such as Dutyion™. One feature of this material is that it expands significantly as it hydrates. The pipe (102) is generally cylindrical, but it is corrugated along its length, with roughly regular ridges (103) and grooves (104). The connector (101) has a side wall (106) defining a substantially cylindrical cavity (107). The inside surface (108) of the cavity (107) is corrugated in the similar way to the pipe (102). When the pipe (102) is in a dehydrated state, the cavity (107) of the connector (101) has a maximum diameter D greater than the maximum diameter B of the pipe (102) and a minimum diameter C less than the maximum diameter B of the pipe (102). The pipe (102) can be inserted in the cavity (107) of the connector in a dehydrated state. When the system (100) then carries water, the pipe (102) hydrates, which causes the pipe (102) to expand and its diameter to increase. This means that the ridges (103) of the pipe (102) expand into the grooves (110) of the cavity (107) and the pipe (102) fits more tightly into the cavity (107) and the seal between the pipe (102) and the cavity (107) is improved.