We used that GTAP-W model – GTAP5 with water resources added – to estimate the impact of hypothetical Doha-like liberalization of agricultural trade on water use. Three conclusions emerge. First, the change in regional water use is less than 10%, even if agricultural tariffs are reduced by 75%. Second, patterns are non-linear. Water use may go up for partial liberalization, and down for more complete liberalization. This is because different crops respond differently to tariff reductions, but also because trade and competition matter too. Third, trade liberalization tends to reduce water use in water scarce regions, and increase water use in water abundant regions, even though there no water markets in most countries.