A settlement tank for use in a water treatment process. The settlement tank comprises a perimeter wall and a base to define a fluid holding region for holding fluid in the settlement tank. The settlement tank may comprise a scraper assembly comprising a scraper for scraping sludge from the base. A support connected to a central region of the base may comprise a mount rotatably mounting one end of the scraper to the support and positioned below an operational fluid level so as to be fully submerged during operation of the settlement tank. A drive mechanism for rotating the scraper assembly about the centre of the fluid holding region may be positioned outside the perimeter wall. An energy recovery device may be arranged to harness energy from fluid flow through an outlet formed in the perimeter wall. A launder trough via which fluid from the fluid holding region can exit the settlement tank may be constructed and arranged to define a walk way along which a person can walk. The launder trough may comprise a barrier wall with a plurality of holes below the operational fluid and scum level and through which fluid can flow to the launder trough.