Many smaller issues are avoidable and also easily repaired. To avoid minor damage to wood floors, be mindful of wet mopping, excess water at entryways, and overzealous settings on humidifiers. This excess water can cause crackling of the finish or even expansion or cupping of the wood.
As soon as you notice an issue with your hardwood floor, you need to act immediately to dry it out. If necessary, remove water from the floor with a water extraction vacuum. To dry the flooring, open windows and use a dehumidifier or fans to pull out the moisture. Do not apply heat to the wood as this can cause further damage. Given enough drying time, the floor may contract on its own.
There are a number of different types of water damage that can occur to hardwood floors, and each requires a different method of repair.
A white stain or haze typically indicates minimal damage to the surface of a hardwood floor. To remove this spot, use light pressure to buff the finish of the wood with a mild, abrasive cleanser and a cotton cloth. Suggested cleansers include whitening toothpaste or automotive polish.
A black stain can indicate greater issues, such as mold growth. To repair, first, make sure that the flooring is dry. Then, tape off the area so that it is isolated during the repair process. Working just up to the edges of your tape, remove the wax and finish using steel wool and sandpaper. Mix oxalic acid crystals in hot water and brush the mixture onto the stained area. Let it dry, brush it off, and repeat this process until the stain is removed. Stain the area to match the rest of the floor, and finish with sealant.
After severe water damage, it is likely that wood floors will have to be replaced. Wood is especially susceptible to mold growth, so you need to ensure that the floor and sub-floor are completely dry. Unfortunately, even getting these floors completely dry at the time does not mean that you may not experience issues with mold at a later date.
If boards have cupped, popped, or cracked, this may be an indication that the sub-floor experienced damage as well. If the sub-floor is damaged, it will also need to be replaced before you can install new hardwood flooring.