The share of piped water supply into the dwelling is higher (38% vs. 23%), while some other sources such as rainwater harvesting did not appear in the questionnaire. Source: Guyana 2002 Census, p. 129  Other sources of water supply for non-potable uses include rainwater catchment (5%); public standpipes or pumps (3%); private wells (1%); rivers, creeks, streams, ponds and springs (11%); and others (3%). According to the 2002 census, only 5% of the population had access to a W.C. linked to a sewer; 36% had access to a W.C. linked to a cesspit or septic tank; 56% had access to a pit latrine; and 2% had not access to sanitation facilities. The census does not allow to determine the type of latrine used, and thus it cannot be deducted from the data what is the share of population with access to adequate sanitation. Sewers only exist in the capital, Georgetown. Regions 7, 8 and 9 in the Hinterland show the highest share of population with no access to sanitation, each with more than 15% of the population without access. Service quality for customers connected to the public system is poor, including low water pressure in most service areas, intermittent supply in all service areas, and a high risk of bacterial contamination due to the fact that about half of the public supplies receive no disinfection. Throughout the coastal area of the country the aquifer that supplies most of the drinking water has a high level of iron, making the water red. Iron removal plants are being built to remedy the problem. Guyana, meaning "land of many waters", is rich in water resources. Most of the population is concentrated in the coastal plain, much of which is below sea level and is protected by a series of sea walls. A series of shallow reservoirs inland of the coastal plain, called "water conservancies", store surface water primarily for irrigation needs. Groundwater, which consists of three distinct aquifers, provides about 90% of the domestic water needs of the country. The groundwater system comprises three aquifers:  From about 1913 to 1993, the head in the "A sand" aquifer has declined by 20 meters. According to a 1998 study by the US Army Corps of Engineers, long-term studies are needed to determine the capability of the aquifer to sustain increased withdrawals. Hydrological data are lacking throughout the country, particularly since the late 1960s when data collection decreased dramatically.