Source: The Great Interpretation of Dreams (Ibn Sirin)
Watering plants or trees in a dream indicates marriage, raising children, or performing a good deed. Watering people indicates kindness to them and spreading knowledge.
Source: Perfuming Humanity in the Expression of Dreams (Al-Nabulsi)
Watering indicates fulfilling needs and gaining sustenance. Whoever sees himself watering a thirsty person, God will relieve his worry.
Source: Signs in the Science of Expressions (Ibn Shaheen)
Watering is interpreted as goodness and benefit. Whoever sees himself watering will attain goodness.