There are two different types of water damage.
The second, more harmful type of water is called dirty water. This water comes from an overflowed toilet, failed ejector pump, broken sewage line, etc. This is hazardous water and must be treated with extreme caution. Still solid fecal matter may still be present, along with clumps of decomposing bath tissue. Because of this, the water damage smell and odor can be unbearable at times. All affected materials ought to be discarded and the affected walls, baseboards, carpet, and pad need to be treated appropriately.
The "least" harmful is called clean water, which comes from such sources as a sump pump failure, foundation crack, appliance leak, etc. It is relatively safe if it has not been sitting untreated for more than 72 - 94 hours. If your water damage has been sitting untreated for over this time, dangerous bacteria have grown and the water should be treated as dirty water. The water damage smell from clean water ought to be nothing more than a musty smell. If its worse, your water damage is probably dirty.
Regardless of what type of water you have, you need to act quickly and decisively. Water damage is progressive, meaning that the longer it goes untreated, the worse the damage becomes. Taking action quick will give you the best chance in mitigating most of the damage, along with being able to salvage water damaged furniture and other personal items. Repair water damage and restore any affected materials ASAP!