Drinking water service coverage, World, 2000 to 2015

Total population using a given drinking water source. At least basic drinking water represents an improved source within 30 minutes’ round trip to collect water;
'limited' constitutes an improved water source more than a 30 minute round-trip away; 'unimproved' is one that by the nature of its construction does not adequately
protect the source from outside contamination; and 'surface' is that from surface water sources.