[header] How to do water aerobics [title] Get a chlorine resistant bathing suit. [step] Water aerobic classes are usually about an hour, so you want to make sure you have a suit that can deal with hour long classes a few times a week. [substeps] You can wear a one or a two-piece suit, but a one piece is probably more comfortable. 
Some gyms might require that you wear a one piece. If you're taking water aerobic classes at a gym, make sure you find out.