Deep drainage below irrigated crops wastes a scarce resource and can potentially lead to rising water tables and salinity. The lysimeter facility at the Australian Cotton Research Institute (ACRI) was used to measure deep drainage at 2.1 m depth under a furrow irrigated cotton-wheat rotation Drainage accounted for 11% of the irrigation. Two distinct types of drainage were observed - matrix and bypass. Bypass drainage was much faster and occurred immediately after irrigation. It accounted for most of the drainage. Drainage could arrive at the watertable at 16 m depth within 15 - 30 days. Bypass drainage was inefficient at leaching accumulated salt, but removed about 6% of the applied nitrogen.