As one of Iran’s architectural and engineering achievements, water mills have had a vital role in people’s life. However, some constraints including drying or low water reserves of their Qanats, and economic deficiencies, have had a negative impact on their public acceptance. As a heritage representing the knowledge of ancestors, and a symbol for the proper use of environment, these constructions are a collection of different sciences and technologies (in the fields of architecture, structure, hydraulic engineering, mechanical engineering, and mining). Various types of water mills were used in Iran from old ages for grinding grains and producing milled powder. The process was especially important in producind flour and its use in baking bread, as the most important daily meal of the nation. Water mills were common where Qanats or rivers were accessible, and windmills were widespread in regions with strong airstream. Like most desert areas, Naein water mills are of Qanat and chimney types due to lack of rivers. Obviously, the depth of the Qanat would prohibit the perception of the water flow, but influence of its power can be seen in moving millstones. The process of bringing water power to the mechanical parts of the mill, and henceforth its exit from the structure is of utmost importance. Hence, there are two important points in architecture of water mills; first the provisio of water in the vortex, and second, the separation of dry and wet areas. Thus, water mills require dry spatial components, such as gate, relating canal, storage, and compartment, and wet components such as chimney, deploying area of vortex, and the incoming and outgoing water canals. Different structures and compositions of spaces are observed in Naein water mills. According to the field survey, it was found that there are only 12 surviving water mills in the proximity of Naein city, and the numerous other have been completely ruined. Therefore, analysis and documentation of the remaining number is of great value.

What is considerable in documenting with these constructions is their remarkable diversity. Despite common principles and applications, the remaining mills have diverse areas, and there are little similarities between them. The positions of the main elements of water mills are also varied. Some of them are totally built underground, some are constructed on the ground, and some have midway positioning. The range of the diversities in a small region is of interest, and its reasons require further investigation. This study tries to identify the effective factors on these diversities, and presents a typology for these water mills. The results of the assessments showed that according to architectural criteria and locations, Naein water mills can be categorized into three different types, namely ground-level mills, manually carved underground and manually carved on clay walls. The type of above-ground mills are constructed on the terrain level, using Qanat water running between the plantations. The manually carved underground mills are constructed to have access to the Qanat, with its water moving in the duct under the ground towards its route and further along to the residential area (in the two water mills of Rigareh and Mehrijan). The third type includes horizontal cutout water mills. The mills of this type are built in places where the differences in ground level have created clay walls, and the mills are constructed horizontally under the ground near the terrain level. The study follows a descriptive method, based on documents and field observations. The technical drawings for the documentation of the water mills are produced for the first time in this paper. Through the documentation and typology of Naein water mills, this study hopes to take steps towards the registration of a significant heritage, and to facilities relevant studies in the future.