Most larger towns and cities get their water from reservoirs in managed watersheds, but some small communities on Vancouver Island, and most rural residents, depend on wells that tap into undergound water supplies.
Underground water, or 'groundwater', is produced by seepage of rainwater, snowmelt, and stream waters into rocks and sediments. Groundwater commonly resides in fractures and holes in bedrock and sediments. Water wells tap into this underground water supply. The quality of groundwater is often good, but it can be damaged by human contaminated water that percolates down from the surface. Some groundwaters are naturally contaminated with elevated levels of iron, hydrogen sulphide, or fluoride.
Groundwater supplies can be depleted by overpumping. The water table drops when more water is pumped from the ground than is replenished. Groundwater can also be contaminated by salt water in coastal areas. A boundary exists between fresh groundwater under land and salty groundwater beneath the Strait of Georgia. Coastal wells near this boundary may pump salty water some of the time. Overpumping increases this problem as saltwater is drawn toward the well.
Fractured mudstone layers like these exposed in road cuts near Duke Point are important groundwater aquifers in the region.
Water From the Mountains
Nanaimo's drinking water comes from melting snow and rainfall that feed two large reservoirs in the mountainous watershed of the Nanaimo River. These reservoirs impounded by the South Fork and Jump Creek dams provide an adequate water supply for both our thirsty population and year-round flow in the Nanaimo River.
Timber harvesting in Nanaimo's watershed can increase soil erosion and thereby the amount of silt and clay in our reservoirs. Silt and clay poses no direct threat, but it does reduce the effectiveness of chlorine in killing potentially harmful water-borne microorganisms. The City of Nanaimo has a comprehensive water-testing program to ensure water quality and protect public health.
