The impurities in the water causes corrosion and provides circuit paths for the electricity which were not in the laptop's operating design and could damage the components. The corrosion starts immediately and is ongoing until it is completely cleaned away.
Using rice to fix water damaged electronics is a myth. It doesn't work. Rice does not fix the problems caused by corrosion Rice is for dinner, not repair
First do not try to charge or to turn on your laptop and then remove the battery as soon as possible from the laptop to minimize any further damage.
There is always power on the motherboard at some points on the board even when the laptop is turned off. The power button is not a power isolating button. Its function is to signal the intentions of the user to the operating system e.g. turn on, turn off, wake from sleep etc. Think of the laptop as being in an extremely low power state when it is off and not that it is disconnected from any power at all.
Then you need to dis-assemble the rest of the laptop and clean all the affected parts using Isopropyl Alcohol 99%+ (available at electronics parts stores) to remove all traces of corrosion and water. If possible do not use "rubbing alcohol" as in some cases this is only 70% IPA or less, can contain additives which may leave conductive residues and is not as effective. If you do have to use it check the label to verify the amount of IPA. The higher the percentage of IPA the better
Here is a link that describes the process. Electronics Water Damage
As always with electronics, especially surface mounted pcb be gentle when handling and especially when brushing away the corrosion. You do not want to remove any components from the board. Remove the shields that may be covering some components as the water may have got in under there. Also any removable modules as well The ends of any flex cables and their connectors need to be cleaned also.
Hopefully after you have done all this the laptop might possibly work correctly again.
Here is a link to teardown video for the laptop, that may help.
If this process seems too daunting, take your laptop to a reputable, professional laptop repair service, experienced in liquid damage repair and ask for a quote for a repair. If you decide to do this, do it sooner than later.
Getting it repaired or replaced is for you to decide. Depending on the cost it may be better to get a replacement as fixing water damaged electronics can sometimes be problematical and not 100% guaranteed. It may work Ok for months and then suddenly start to have problems. Then again everything may be OK.
There are a number of repairers I know who refuse to fix water damaged electronic devices simply because they cannot provide the 100% guarantee that it is OK that most customers want to have.
At least with a replacement (presumably new and not a refurbished unit - although perhaps it may come with a warranty of some kind) you know that it should be OK with no previous damage to worry about. Again cost may be the contributing factor that you have to decide on.