In the tragic event of getting something like a phone wet the outcome is rarely good. However, the chances greatly depend on how quickly you take action. While liquid damage is completely dictated on a case by case basis, at least part of the time, it can be fixed as long as you don't wait too long before and don't do anything to damage the device further.
While any kind of liquid can damage electronics, some are more severe than others. Acidic substances (such as OJ, soda, beer, etc ) can eat away at delicate electronic components and failure rates with these type of liquids is much higher than coming into contact with water.
If the iPhone was exposed to water in the last day then it is VERY unlikely the phone has completely dried out.
So, if the device is not turned off, do so now.
Things you should NOT do:
Do NOT try to turn it on again for the moment as this may cause further damage.
Do NOT plug it into your charger. you can short circuit the logic board or other internal components. The more you try to turn it on and use it during this important window of treatment increases the likelihood of further damage.
Do NOT use heat (such as a hair dryer or heater) to further the drying process as they may contribute to further failure.
Things you SHOULD DO:
All iPhones, iPads, and iPods have water sensors in them. You can check the dock connector, headphone jack or SIM slot with a flashlight to see if the sensors are triggered. The sensors should be white. If they have turned red, liquid has gotten into one of the ports at the very least.
React fast. If you value the device, get in contact with a reputable repair facility immediately. If you don't have anyone local that you can trust, try:
http://www.thepoddrop.com/ (which also has a few store locations)
Both offer free diagnostics and economical repair services.
If you absolutely can not afford a repair and the device has ONLY come into contact with plain water, you may try the following.
Enclose the device in a plastic bag with a cup or two of dry, uncooked white rice. It's important that you leave it in there for AT LEAST 48 to 72 hours or more in order to pull the moisture out of the internal components and into the rice.
There is nothing you can do to guarantee full functionality and little more you can do, personally, to further improve the situation at this point in time but to wait and see if the phone works once it is completely dry.
Professional service is always preferred but the above may save devices with minimal contact to water.
Please note: I can provide expert advice and information only - not for the successful repair of your iPhone. When troubleshooting electronic issues, sometimes the final diagnosis is that it is a physical defect in nature and the ‘answer’ such as in this case may be a recommendation to seek out repair from an authorized service center if the defect in question is not considered “user repairable”. This may be a frustrating answer and I do sympathize but please don't shoot the messenger.