The unremitting trends of increasing population, urbanization, diminishing water supply, and continuing climate change have contributed to declining stocks of arable land per person. As land resources for agriculture decrease, policy makers are faced with the challenge of sustainability and feeding the rapidly growing world population which is projected to reach approximately 9.7 billion in 2050. Solutions for improving future food production are exemplified by urban vertical farming which involves much greater use of technology and automation for land-use optimization. The vertical farm strategy aims to significantly increase productivity and reduce the environmental footprint within a framework of urban, indoor, climate-controlled high-rise buildings. It is claimed that such facilities offer many potential advantages as a clean and green source of food, along with biosecurity, freedom from pests, droughts, and reduced use of transportation and fossil fuels. In this article, the issues involved are evaluated together with potential advantages and disadvantages. Possible implications are identified for consideration by policy makers and to facilitate further economic analysis. ARTICLE HISTORY

As competition among industrial, agricultural, urban and environmental sectors for freshwater intensifies, wastewater is frequently being seen as a valuable resource rather than mere waste. Furthermore, wise reuse of this water alleviates environmental concerns attendant with its discharge to coastal environments and inland waterways. Globally, around 20 million ha of land are irrigated with wastewater, either neat or partially diluted. This figure is likely to increase markedly over the next few decades in response to rising levels of water stress in inhabited catchments -in 1995 around 2.3 billion people lived in river basins considered to be water stressed and this number is expected to increase to 3.5 billion by 2025. Here we review the current status of wastewater irrigation by providing an overview of the extent of the practice in different parts of the world and through an assessment of the current understanding of various issues relating to sustainable and safe management of irrigation with wastewater. A theme that emerges is that wastewater irrigation is not only more common in water stressed regions such as the Near East, but the rationale for the practice also tends to differ between the developing and developed worlds. In developing nations the prime drivers for wastewater irrigation appears to be livelihood dependence and food security, whereas environmental agenda appear to hold greater sway in the developed world. The following were identified as key areas requiring greater understanding for the long-term sustainability of wastewater irrigation: (i) accumulation of bio-available forms of heavy metals in soils, (ii) an understanding of the balance of various factors affecting the environmental fate of organics in wastewater irrigated soils (iii) the influence of reuse schemes on catchment hydrology, including transport of salt loads, (iv) risk models for helminth infections (pertinent to developing nations), (v) microbiological contamination risks for aquifers and surface waters, (vi) transfer efficiencies of chemical contaminants from soil to plant, (vii) effects of chronic exposure of people to chemical contaminants in wastewater, and (iix) strategies for engaging the public in wastewater irrigation schemes.