KiwiRail shipped about 300,000 litres of drinking water into Christchurch overnight.
Water supplies in the city were severely disrupted by the earthquake on Saturday. Residents are being told to boil all drinking water.
KiwiRail's says the Fonterra has made a number of its rail tankers available for transporting water to Christchurch from Temuka.
Chief executive Jim Quinn says it's not yet clear where and how the water will be distributed, but the company thought it was worthwhile getting supplies into the city.
Mr Quinn says it will be Monday at the earliest before the railway line between Christchurch - Rangiora will be open again, due to damage around Kaiapoi.