In the southern and most populated part of the province, the rivers rise in the mountains and then flow southwards. The biggest river, the Fraser River, flows into the Pacific Ocean through Vancouver. The other major rivers are the Columbia River, which flows into the United States, and the Peace River, which flows to the Arctic. Abundant precipitation occurs in the Pacific Maritime ecozone, which includes the coastal rainforests. However, in the dry interior, where annual precipitation is less than 400 millimetres, water is scarce for irrigation and domestic use.
Most precipitation falls in the winter months, and little during the summer.
Water is often stored in reservoirs created by small dams. Most of these reservoirs are licensed for irrigation use. They are also used for recreation and as habitat for fish and wildlife. Irrigation or municipal districts in the Okanagan and Kootenay regions supply water to farms through pressurized lines for both irrigation and domestic use. Ponds and dugouts are rarely used for irrigation unless they are replenished during the summer by springs, seepage, or rainfall runoff.