New York City Water Tunnel No. 3 is the largest construction project in New York history. It is being built by the New York City Department of Environmental Protection to provide New York City with a third connection to the Upstate New York water supply. Upon completion, the tunnel will be more than 60 miles (97 km) long and will cost over $6 billion. Construction began in 1970 and will not be completed until 2020.
After the heist of gold bullion in the Federal Reserve Bank and hauling them by dump trucks, Simon Gruber and his men took the New York City Water Tunnel No. 3 to go to the Catskill Mountains. Several men tore up the tube to go through the tunnels. Simon has Nils and Klaus stand guard in the tunnel if case of any trouble.
Then John McClane shows up with trucker Jerry Parks. McClane learns from the foreman that Simon's men tore up the tube to enter the tunnel and they will be heading to the cofferdam near the Saw Mill Parkway about 20 miles away. McClane has Jerry drive him to the tunnel as Zeus went to Yankee Stadium. As Jerry was driving, he gives McClane a tour of tunnel 3. Then they stopped when they notice a truck blocking their path. Jerry honks his horn and the truck still doesn't move. McClane finds this suspicious and decides to investigate. He takes Jerry's hardhat and jacket, disguising himself as an aqueduct security guard and makes his way to the truck. Inside the truck, Nils and Klaus wait for McClane to get close enough so they can kill him. Unfortunately for them, McClane beats them to the draw and fires several shots into the door of the truck, killing them both. He then begins to search Nils' body and finds a radio and 10 quarters. He tells Jerry to find his boss Walter Cobb to get aqueduct and find out who the 21st president, to which Jerry answers that it was Chester A. Arthur. McClane heads out to pursue Simon and his men.
As all of the trucks passed by, one of the temporary bridges fell out of place. Then Mathias Targo, who was driving the truck with Simon and Katya, says they arrived in the cofferdam. Simon tries to check in with Nils and Klaus to come up now. But McClane taunts Simon that they are both dead as well as the four men down in the bank. Simon tries to make a deal with McClane, but he refuses to do so. As they exited the tunnel, Targo berates that he should've toyed with McClane since he'll jeopardize the mission and the contract. As Targo was about to get McClane with some men with him, Simon sees the suitcase bomb that was in Tompkins Square Park and tells Targo to blow the dam so they can drown McClane. Targo and some men planted the bomb in the cofferdam.
McClane stops the truck when he sees one of the temporary bridges went down. He tries to get it back up, but to no avail. As he was heading to the dam by foot, he sees a huge flow of water coming at him. McClane rushed back to the truck and took off. McClane tries to drive away from it, but the water was coming in too fast and it soon hit the truck. He goes on top of the truck and grabs on the vent shaft with the water hitting him. As McClane was climbing up in the vent shaft, the water pushes him upward in the manhole and he lands in the water-filled ground near the manhole just as Zeus arrives who notices him from the window of his car. It is unclear how much the water affected the construction of the Tunnel 3 at that time.