The common problems are clogged drains and toilets to fix loosen clogs using air pressure, move them up down to create suction, use a tweezer or pliers to grab the clump and remove it from the drain, chemical drain cleaners use to remove the blockage with a plunger. Leaky faucets and pipes can be a DIY job, but replacing the washer need special tools, turning faucets on and off slowly, and avoiding excessive pressure.
water heater issues look at the temperature settings to ensure wasn't turned down if you think mineral deposits are the issue, drain the water tank flush out the floor sediment. low water pressure if you think build-up is the problem, unscrew the end on the faucet for cleaning, soak the aerator or showerhead, put vinegar in a plastic bag, and let the aerator sits in the solution. running toilet check each component to find the specific problem. Ensure the fill tube, a thin flexible tube inside the tank, adjust the float fill a valve shuts off properly, attached a flapper to get the proper length and to ensure not tangled.