The correct water temperature for your dishwasher depends on the washing phase. When water enters the machine, it should be around 120 degrees Fahrenheit, but no hotter than 150 degrees. During the wash cycle, the machine will heat the water to between 130 and 140 degrees. If your dishwasher has a sanitizing cycle, the water can reach a temperature of up to 180 degrees.

It might be time to buy a new dishwasher for your kitchen if you consistently notice a significant amount of water left over after a cycle, indicating potential drainage issues that are becoming persistent or costly to fix. Visible rust, especially on the interior tub or racks, suggests internal corrosion that will likely worsen over time and can compromise cleaning performance. Additionally, if your dishes are coming out excessively hot after the drying cycle, it could point to a malfunctioning heating element or thermostat, which can be an energy inefficiency and a potential safety concern, making replacement a feasible choice.

Yes, a dishwasher needs an air gap to prevent backflow. Additionally, in many locations, air gaps or another measure to prevent backflow are required for building code compliance. There are alternatives to an air gap, like a Studor vent or a loop and trap design, but an air gap is the simplest and most popular solution.  

A dishwasher can help save you significant time when it comes to getting your dishes clean. It can also get your dishes more hygienically clean than washing by hand due to higher water temperatures and specialized detergents, effectively sanitizing them and reducing the risk of foodborne illnesses. Compared to hand-washing, a dishwasher typically uses less water and energy to clean the same amount of dishes, making it a more resource-efficient option.