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The global demand to increase food production from underperforming, water and nutrient limited soils is increasing, which has resulted in an increased dependency on water for irrigation. As fresh water is a finite resource, the increase in irrigation use has resulted in competition between water used for municipal purposes and that used for food and fibre production for an increasing global population. An opportunity exists to improve the efficiency of both urban and agricultural systems by taking green waste compost generated in urban centres and incorporating it into agricultural soils with poor water retention, thereby increasing the ability of these soils to efficiently retain irrigation water for plant use and also to capture a greater volume of water from rainfall. Addition of amendments to soil changes the pore space. The magnitude and cause for this change depends on amendment type, application rate, soil type and climatic conditions. The aim of this research was to determine if the incorporation of municipal compost (MC) can increase the quantity (total volume) and concentration (total volume per unit volume) of soil pores that hold readily available water (defined as macro-mesopores of 30-3 pm diameter) and plant available water (defined as mesopores of 30-0.3 [micro]m diameter). We hypothesised that increases in total porosity would be positively correlated with MC application rate and increases in water holding porosity (macro-mesoporosity and mesoporosity) would be positively correlated with decreasing MC particle size due to the creation of inter-particle pore spaces < 30 [micro]m in diameter. The MC was screened to three different maximum particle sizes--MC4 ( Additional keywords: municipal compost, pore volume, porosity, soil, water. Received 21 June 2019, accepted 25 November 2019, published online 18 December 2019, Introduction Globally, there is increasing demand for fresh water, which presents a challenge as water is a finite resource. Crop irrigation currently consumes 70% of global water extractions, making it [...]