Whenever you buy something from another person, there is always a chance that the item in question may have some water damage. Water damage can happen for many reasons and are to be carefully considered. The kind of object you plan to purchase is just as important as when it was damaged. To keep things simple, we will assume that the water damage was from a broken pipe of clean water in a home.
Plastic surfaces can take a fair amount of water and can be water-damaged only a small bit or nothing at all. The most important thing to remember is whether or not there has been some mold growing. If you purchase something made of plastic that was in a flood, there is a good chance that it can still be used after some deep cleaning. Things of this nature are simple children's toys, highchairs, storage bins and even some CDs.
Wooden surfaces that show signs of water damage can have some warping on the piece that may or may not affect the structure of the item. Things that are made from particle board (very small pieces of wood that are compressed together) may not be salvaged. The small chunks of wood take on water and expand at different rates because they may be made out of differing woods. Hardwood furniture can be reconditioned if the wood isn't warped out of place a whole lot. In the case for a warped top to a stool or table, the top may be able to be flattened out so that it can be used again. The one thing to remember when buying water-damaged wood pieces is that it can hold in mold that may never go away.
If you are looking at buying some textiles affected by water damage, remember that they may have grown extensive mold that may never recover. Some items that are not damaged much can be washed and recovered with great success. Some of these may be curtains and sheets, since these fabrics typically don't have a lot of complicated designs. If the water damage is extensive, or if it has been lying around for some time, it may be best to not buy that item as it may harbor mold.
The best items that can be bought even if they went through water damage and still be used just like before are usually kitchen items. Since kitchen equipment is made to endure moisture and time, they are perfect for recovering in the event of a flood of some sort. Pots and pans are great, as well as utensils and glassware. The only thing that can go wrong with this one is if it has been sitting around for a while and rust starts to form. The rust may be cleaned off and all is well, or may have gone further and is now affecting the actual structure of the piece. Anything made from glass such as vases, stemware, tumblers and so on is considered to be fair game.
Electronics are to be considered bad buys if they have been water-damaged. If the item was unplugged and cared for rather quickly before any rust sets in, it may still be salvageable. Don't count on this, however. The same goes for audio and video tapes and vinyl records. Water tends to warp these.
All in all, there is some risk associated in buying water-damaged items. It is important to consider how the item is going to be used and your health and safety are considered.