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.