Box 4.2 describes three idealised scenarios of efficient water allocation between urban and rural consumers (for the case of a renewable resource). Policy makers might in some cases favour the equity and fairness of the resulting allocation profiles over their economic efficiency. For example, low-income farmers in water-stressed regions may not receive enough water to sustain their livelihoods; an equitable allocation would therefore require shifting water resources to the more vulnerable groups in society at the expense of economic efficiency. Chapter 5 will further emphasise procedural equity, i.e. participation of all stakeholders in the way water is managed as a whole, especially when it crosses urban and rural areas.