Dehydration [Hazard]

Source: D&D 5.2 SRD Rules Glossary

A creature requires an amount of water per day based on its size, as shown in the table. A creature that drinks less than half the required water for a day gains 1 Exhaustion level at the day's end. Exhaustion caused by dehydration can't be removed until the creature drinks the full amount of water required for a day. See also "Exhaustion."