You can find a ton of recipes on the internet for sea salt hair spray to give you beach-wavy hair. Most of them use epsom salt (magnesium sulfate). Although magnesium sulfate will create waves and curls, it can be really drying and can cause your hair to be brittle with prolonged use.
I have discovered a more gentle, moisturizing recipe that will still give you the beach-hair you desire without drying out your locks! I use magnesium oil instead of epsom salt. Magnesium oil is much more gentle, yet still provides curl enhancement. I also sometimes add it to my homemade hair gel.
Place a few drops of magnesium oil into the spray bottle. I have short, fine hair, so I only need a couple of drops. A little goes a long way. If you have longer or thicker hair, you could add a couple more drops. Then add the distilled water to fill the bottle. Add several drops of hair oil such as argan oil, coconut oil, or a blend such as this one by La Bella Figura or my newest favorite by Tabitha James Kraan.
You can play around with the measurements to get the right balance for your hair type.