Towards zero liquid discharge: the use of water auditing to identify water conservation measures

•Multiple methods can be used to determine historical flows in water audits.•Water auditing indicates areas for conservation, such as alternative water sources.•Results of water audits can inform both plant retrofits and new infrastructure.•Water auditing contributes to achieving zero liquid discharge.

Water is economically cheap, which fails to consider its intrinsic environmental and social value. However, given the uncertain future around the availability of water resources to provide industrial, environmental and social services, water conservation is now of significant concern to industries across the globe. Recently, an extension of water conservation has emerged as zero liquid discharge, whereby no water at all is released from industrial processes, regardless of its quality.Water auditing is a tool that can be used to identify water conservation strategies, ideally leading to zero liquid discharge. This article discusses a water audit conducted on a sodium cyanide plant, where flows were determined using historical data, proxy data, and known scientific relationships. Water quality throughout the process was defined as contaminated or uncontaminated. From this simple audit, two major water conservation measures were identified and modelled which could reduce inputs and outputs by ∼40%. These were the reuse of rain water falling throughout the plant's boundaries instead of demineralised scheme water, and the improvement of the efficiency of one of the cooling towers.Such a methodology could be easily applied by other industries so as to improve their water conservation. The auditing method may lead to suggestions of conservation techniques for implementation either through retrofitting existing plants or contributing to the design of new ones.