Given the critical role of water in supporting life, it is not surprising that almost all planetary missions are examining water in the solar system. These include, but are not limited to:
NASA Oceanography Missions
Part of NASA's mission is to develop an understanding of the total Earth system; our oceans play a major role in influencing changes in the world's climate and weather. Today there are several ocean-observing satellite missions and an extensive scientific research community studying these data.
Lunar Reconnaissance Orbiter
The instruments on this mission are studying and mapping the Moon globally; one of its key objectives is to map the locations and amounts of water on the Moon. It has discovered the widespread presence of water ice in large areas of the lunar south pole.
Mars Exploration Rovers
The big science question for the Mars Exploration Rovers is how past water activity on Mars has influenced the red planet's environment over time. Major discoveries of evidence of past liquid water on the Martian surface include a stratified pattern and cross bedding in Martian rocks, and minerals that form in the presence of water.
Mars Reconnaissance Orbiter
Mars Reconnaissance Orbiter is designed to track changes in the water and dust in Mars' atmosphere, look for more evidence of ancient seas and hot springs and peer into past Martian climate changes by studying surface minerals and layering. Among the mission's major findings is that the action of water on and near the surface of Mars occurred for hundreds of millions of years.
Cassini launched to Saturn in October 1997, and has been in orbit around the ringed planet since 2004. Among other things, it has extensively studied the water on Saturn's moons, including Enceladus and Titan. Its mission to study Saturn, its moons and rings has been extended to 2017.