In my opinion, it is not all in the water but if you know what you are doing you can recover a heck of a lot of jewelry and coins in the water.
I do a lot of water hunting, but I always try to keep my metal detecting time balanced to around 50% beach hunting and 50% water hunting.
That way I get the best of both worlds by not completely ignoring half the beach.
I know many "Experts" on the detecting forums say its all in the water and to only water hunt, but that is very bad advice for beginners.
You should always learn how to use your metal detector on the beach, before venturing into the water.
Imagine how long it would take you to learn how to set your metal detector controls, sweep speed and search coil control in the water.
Unfortunately that is how many people get into water hunting, not taking the detecting skills you can only learn on the beach into the water.
My latest book "Water Hunting" shows the connection between beach and water hunting and how great beach hunters make top notch water hunters.
I took a client out this morning for an Excalibur training session, it was pleasantly surprising to know that he wanted to learn how to use his Excalibur on the lower beach before starting water hunting.
Target recover skill's are an over looked part of water hunting, if you are proficient recovering targets in the wet sand with waves rushing over your search coil, you should have no problem recovering targets inside the water.
I always know when I am following a novice water hunter, by the big wide holes left behind by someone who has not learned to pinpoint targets, I have found plenty of jewelry in and around clumsily dug holes inside the water.
Metal detector control settings are the most important reason to learn how to metal detect on the lower beach before water hunting.
Water hunting is easier when you know how your metal detector handles itself on the lower beach next to the waters edge.
You can make control adjustments and know why you are using those settings, instead of using a bunch of safe settings passed around and used by everyone on an internet forum.
Metal detector control settings for water hunting, usually mirror lower beach settings, but tweaked to suit the surf conditions.
In my opinion, both the beach and water are equally good places to find jewelry and coins.
You just have to use your knowledge of local beaches and site reading skill's to determine where your best chance of finding jewelry or coins is going to be.