The Belgrove Railway Windmill is a rare example of a once common feature on New Zealand's railways. In the late nineteenth and early twentieth century, tanks were strategically placed along New Zealand's railway lines to supply steam trains with the vast amount of water required to power the engines. Where the only water available was below ground, windmills were built to pump water the water up and into the waiting tanks. Dozens were erected at railway stations throughout the country. The Belgrove Windmill was built in 1898. When the line connecting Belgrove to Nelson was first opened in 1881, locomotives were supplied with water pumped from a spring by steam engine. In 1895 the Railway Department began extending the line through to Motupiko, and in 1897 the Department relocated the Belgrove Station to bring it into alignment with the extended railway. To obtain water at the new site the Department erected the Belgrove Windmill the following year, a 'massive structure' that was large enough to supply the steam engines and the entire town with water. The Belgrove Windmill is based on a standard plan designed in 1892 by the Railways Department Acting Resident Engineer Daniel McIntosh (1860-1926), and draughtsman George Alexander Troup (1863-1941). The Belgrove Windmill structure is simply, yet ingeniously designed. It consists of a 4.8 metre (16 foot) wooden sail that was set on a 12 metre (40 foot) wooden tower. The sail powered a pump at the bottom of the tower which drew water up from an aquifer two metres below ground into two large holding tanks at each end of the railway yard. The mill's operation was controlled by valves fitted to pipes that were connected to the holding tanks. Hollow metal balls, which rose with the water level, blocked the valves off when the tanks were full, preventing water from entering. The overflow of water then poured into a wooden bucket connected to the sail. When the bucket was full its weight pulled the sail out of the wind, effectively stopping the mill. The bucket emptied after an hour through a small tap and, once empty, it would rise up the tower, moving the sail back into the wind. If the tanks remained full, the bucket would refill and stop the mill. The system required little maintenance and was protected from damage by a governing plane that turned the sail out of high winds. In the 1920s, the transition from steam to electric trains rendered the railway mills obsolete, and the Belgrove Windmill is now one of just two in existence. In 1922 the Belgrove Station was closed, despite local opposition, but as the line remained open the windmill continued to function. When the Belgrove line, also known as the Midland railway, was closed 33 years later in 1955, most of its associated railway buildings and structures were dismantled. The Belgrove Windmill was retained because it was used for domestic water supply. The mill ceased operating prior to 1969 and was leased from the Crown by the Nelson Historical Society. The mill was restored in 1978, and again in 1992, and is now actively managed as an historic asset by the Department of Conservation. The Belgrove Windmill has national significance as a rare relic of a once common system of water supply on New Zealand railways. It is a visible link with the steam locomotive and provides physical insight into their operation. As such, the windmill reflects an important aspect of New Zealand history. The windmill has architectural importance as an early example of the work of Troup, who later became Chief Draughtsman for the New Zealand Railway Department. The windmill's simple, effective design has technological interest. As one of the few remaining relics of the Midland Railway, the windmill is of local significance. The highly visible structure is a landmark in the Belgrove area and it is held in high esteem by the public.