Next summer, the rain in Spain will not stay mainly in the plain. Digitally controlled sheets of falling water will form the walls of a pavilion conceived and designed at MIT for Expo Zaragoza 2008, an international exposition focused on water and sustainable development.

Pipes fitted with rows of closely spaced solenoid valves will be suspended in the air and act like a large ink-jet printer that controls not ink but droplets of falling water. Computer controls will open and close the drip-proof valves to create liquid walls with gaps at precisely specified locations. The walls will function as giant digital display "screens" that continuously scroll downward, with the finely controlled gaps in the water forming text, images, and interactive patterns. Equipped with sensors, the walls will detect approaching people and open to allow them through.

The pavilion's roof, made of a composite material sheathed with waterproof stainless steel and covered by a thin layer of water, will be supported by hydraulic pistons, so it can be lowered in windy weather and dropped to the ground when the pavilion is closed.

"The dream of digital architecture has always been to create buildings that are responsive and reconfigurable ... , spaces that can expand or shrink based on necessity and use," says Carlo Ratti, head of MIT's ­SENSEable City Lab, who led the design effort and worked with the class that conceived the water wall. "It is not easy to achieve such effects with concrete, bricks, and mortar. But this becomes possible with digital water, which can appear and disappear."