Composite sinks are made of different materials that include polyester or acrylic, quartz or granite and resin. These sinks can be more scratch-resistant than other types of sinks, especially the granite composites. You can remove most stains from composite sinks with a little bit of effort.
Saturate a cloth in vinegar and set it on any hard water stains for up to 30 minutes. Rinse the vinegar off with warm water and dry the composite sink with a towel. The vinegar should dissolve the stain.
Dilute bleach with a mixture of water. The ratio should be 1 part water 1 part bleach. Allow the mixture to sit in the composite sink for an hour. Rinse the sink with clean warm water and dry it with a cloth. This will remove tea, coffee or other discolorations in the sink.
Mix 3 to 4 tsp. baking soda with 2 tsp. water to create a paste. Scrub any stains on the composite sink with the paste and a cloth. Rinse the paste off with clean water and dry the sink with a clean cloth.