My iPhone 5s battery doesn't last?

My phone will be at 100% then within 30 minutes it will be at 20 then when I plug it it it says this accessory is not available a makes it stop charging I did drop it in water about a month ago but i put it in rice and it worked fine until about a week ago

Rechargeable batteries wear out and die depending on how frequently you charge/use them. ISheep must buy a new phone when this happens as the batteries are sealed inside the device and can only be replaced by Apple. The other manufacturers (Samsung, HTC, etc.) allow you to simply buy a replacement battery and replace the one in the phone very easily.

Try different chargers. If that doesn't help, get a new battery

Maybe there's something wrong with the battery. This happened with my old iPhone before. However, no place really sells replacement batteries. Don't go on eBay because it will just be a waste of money (been there, done that) but if you've only have had your phone for a short period of time, Apple could give you a new one for internal damage (if could not be fixed). That's how I got mine fixed. If the battery isn't the problem, maybe your charger doesn't work? Anyways, I hope that helped. The same thing happened to my sister's (which is now mine) because she charges it too much but apple have her a new one.

If it got any water inside, it's probably suffering from corrosion that's shorting things out…
(The "rice" stunt is a complete waste of time, it only dries the outside).

As it's still working to some extent, it's possible a phone repair shop may be able to clean it up and get it working again. Apple are unlikely to do that, it's not covered by warranty and they are in the business of selling phones.

However, as it's only six months old, it would not hurt to try at an Apple shop - just say it's got battery life problems and see what they do. If the mention water damage, plead ignorance.
The worst they can do is send you away with the phone as it is.

(For info, new batteries for iphones are readily available from ebay etc., and fitting one takes just a few minutes).

[Electronics designer and programmer for 40 years].

Oil it's fine but… It can cost some money to repair the thing. Or, you can buy a new one. Consult your gsm doctor.