The design of lining systems for the containment of liquids, for example to contain the leachate generated within a landfill, has become rather sophisticated, employing state-of-the-art technologies from such disparate disciplines such as geotechnical engineering and polymer science. The objective, and to a confident degree, the achievement, has been the prevention of contamination of groundwater and in particular surface waters that support humans and animals alike. The technology involving the design of these containment systems has progressed to a point that the integrity of containment can be relied on over the long term. Double lined systems provide an additional benefit of enabling the quantification of the performance of the lining system by the detection of leakage through the upper liner. The difficulty, however, lies with the qualitative evaluation of the system how much leakage is a little? a lot? too much? This paper addresses this issue and discusses reasons for using Leakage Ratio, a ratio between leachate collection rate and leachate leakage rate, in landfill lining system design.