Water, electricity, and ammonia (artificial fertilizer) are essential for human welfare. The self-sufficient and sustainable productions of them from renewable resources are indispensable for social security and the future society. In this study, we proposed the Water-Electricity-Ammonia (WEA) scheme that produces electricity, freshwater, and ammonia and supplies them at a certain ratio. We investigated the life cycle CO2 (LCCO2) emission from the case of inland cities in arid/semi-arid regions that obtain the three products (electricity, water, and ammonia) generated by photovoltaic (PV) and seawater obtained through a pipeline connecting the ocean and the cities. This study unraveled the necessary condition to reduce LCCO2 emission: the allocation ratio of PV electricity for the three productions and the geographical conditions of inland cities. To reduce LCCO2 emission, allocating PV power to seawater desalination is suitable if the city is in a lowland area, and ammonia synthesis is preferable if the city is in a highland area. Note that the WEA scheme applied to most inland cities, even in extreme geographical conditions, reduces LCCO2 emissions compared to conventional production methods by optimizing the PV allocation of electricity, freshwater, and ammonia production.