however because not all of this water is accessible for human use the term water supply is typically used to refer to the amount of water that is accessible to a demand centre and can be delivered reliably and sustainably with respect to the environment or the finite resource base wrg and it is water supply that is of primary interest when addressing the risks of water shortage at least in the short and medium term for nonoecd countries this typically involves increasing access to water for basic consumption and sanitation something that is provided through investment in water supply and delivery by contrast in many oecd countries the vast majority of the population already has access to a reliable water supply and considerable water infrastructure already exists investment in water supply for instance is needed to replace ageing infrastructure meet increasingly stringent water quality controls and manage extreme weather events oecd