Could I hand sew a bathing suit?

Anything can be sewn by hand. However, it will be a lot easier, faster, and more professional to do it with a sewing machine with a stretch stitch. If you don't own a machine, talk to a dealer about renting one. Or if you're in the market for buying one, ask the dealer about trying one out.

You'll have to use hand-sewing stitches that provide the "give" that the fabric requires. You'll also have to stretch the seams as you sew them to make sure the stitches don't break.

Sewing A Bathing Suit

Hand sewing a bathing suit is not a good idea. It would be difficult to get the stitches close enough to to make them secure enough so that the seams do not come loose. Its really something that needs to be done by machine.

Old school stitching. Check out your local cloth shops and see if there are any Tailors or Seamstresses (that looks spelled wrong but it's not lol) If you ask they may be able to show you. If your really interested Both those Arts are disappearing, If it is something you like it will be sought after by the affluent in years to come.

Good luck.