Explore the waterworks and Buy infobot from mechanic are missions in Ratchet & Clank. An unassigned mission, Ratchet explored the nearby waterworks after crash landing on planet Novalis, before the blarg would be able to take them from the planet, eventually running into the Mechanic for the first time. The Mechanic offered to sell the two an infobot, which contained coordinates for planet Aridia, for 500 bolts so that he could evacuate the planet as well.
Instead of heading down the nearby elevator, for the mission "Find a new ship", turn around and head into the large passageway with water quickly flowing in your direction. Said water forces you to take an impromptu path consisting of falling stalactites and hydraulic platforms. At the end, through a doorway, are several peckbots. Destroy these using either your OmniWrench or Bomb Glove, and head into the next room. You will now be spotted by some birdbots, therefore you should take these out as you cross the gap of water and smash up any crates for bolts.
You will then continue to the next larger room, where a larger gap of water will bar your way. This is a distance too great to jump, forcing you to swim to the lower steps on the right end and climb up from there. This will have to be done again for the next jump as well, except this time, the steps are located on the left end. Afterwards, climb the nearby hydraulics to reach a thin walkway near the ceiling. Carefully follow it to the next and final room. After the cutscene featuring the Mechanic, you will have completed "Explore the waterworks" and will be given the mission "Buy infobot from mechanic". Pay him the required 500 bolts and approach the sewer pipe he just slid down. Simply hop in and let the current carry back down to the outside, to the starting area.