Feathers that are pulled out completely, may grow back at any time. Feathers that are broken off, only grow back during a molt. So, feather damage done by roosters, often doesn't grow back until the hen molts. This is the time of year for chickens to molt, though, so your hens may be trying to regrow feathers.
If other chickens are pecking at a hen's new feather growth on her back, you can put a chicken saddle on her, to protect the feathers as they grow in. It's a little cape, with elastic loops to go around the hen's wings. It's primary function is to protect a hen from the rooster's spurs during mating, but can also protect bare skin from sunburn or growing feathers from being picked.
If they're low in salt, that is supposed to be one cause of picking, according to some poultry literature. If they're not low in salt, then adding salt does nothing. I would never offer salted water, without offering normal water, either, especially if you are just experimenting. I don't think a lack of salt is normally the problem in chickens fed a commercial layer feed. That's why I would not offer only water with salt added. I'd give them a choice.
I'd wonder if they were getting enough protein, especially the amino acid methionine. It's a large component of feathers. It's also most lacking in plant based proteins and most common in animal based proteins. Chicken feed these days have mostly gone to a plant protein only formula. I know that my own chickens don't seem to do as well feathering up, as they did on the older formulas. Free ranging helps a lot with that. Animal proteins, including fish meal, bugs and worms have methionine. Sunflower seeds do, also. You might want to look at their diet.
Other things to look at are how much space they have and giving them things to do, if they're confined.
