What's that bag full of water they're always injecting us through an IV with while in the hospital?

You’re right that its saline, but its not sterilsed water (though Im sure you’re right about the sterilised part also). Its fluid containing electrolytes, similar to the fluid in your body.

Its just saline water

The bag typically contains an isotonic solution. Isotonic means that it has the same osmotic pressure as the fluid in our cells so it won’t cause them to swell or to shrivel. In the US the most common fluid is Lactated Ringer’s Solution. Ringer was a British doctor who formulated a solution that allowed frog hearts to survive longer outside the body. Later lactate was added to buffer pH giving us Lactated Ringer’s Solution. Normal Saline is another isotonic solution commonly used. Saline with 5% dextrose is also common. IVs can be used to prevent or treat dehydration when the patient can’t take enough fluid by mouth. Also medications can be given intravenously themselves or mixed with IV solution. Prior to most procedures IVs are started so if IV meds are needed during the procedure they will already have a line.

Fluid = water containing those things. My brother has to use saline when he gives himself his needle three times a week.

No. But sometimes i wish they could do that to me.