"What is the industry best practice for removing water from the oil reservoir of a piece of equipment? For example, routine oil analysis reveals 3,000 ppm of water in a gearbox oil reservoir of 15 gallons." 

Several technologies exist for removing water from oil, including vacuum dehydration, centrifugal separators, jet-dry devices, headspace dehumidification, aggregate adsorption media and hygroscopic polymer impregnated filter media.

The oil type, volume of water, size of the reservoir and several other factors dictate what technology should be employed for a given situation.

At approximately 0.3 percent water in a 15-gallon sump, you have nearly 5 to 6 ounces of water either dissolved and/or emulsified in the oil. Given the application, I would either use a portable vacuum dehydrator or a hygroscopic polymer impregnated media filter.

Filter the machine offline, preferably while it is operating. Be sure that the plumbing in your decontamination rig is full of new oil (the type used in the gearbox). Before filtering, open the drain valve to get rid of any free water (undissolved and unseparated water that can settle to the bottom of the sump).

If you have some free water in the bottom of the sump, you will need to estimate the volume of free water and add it to the estimate of 5 to 6 ounces. You can do this by estimating the volume in the sump below the lowest point of the drain port (L x W x H). If the drain port is at the lowest point in the reservoir, the volume will be zero. However, most gearbox drain valves are set slightly above the bottom.

If you employ hygroscopic polymer media elements, you need enough water-holding capacity to get rid of the dissolved and emulsified water, plus the free water that will become suspended during decontamination.

You will probably be drawing from the drain port, so this will suspend the water. In addition, drying the oil will lead to free water being pulled into the dry oil via osmosis.

Of course, in addition to removing the water, perform root-cause analysis to find its source. Breathers, seals and new oil are common culprits.

The effects of water on the oil are often overlooked. Excessive water contamination can result in premature oil oxidation and promote the buildup of sludge and varnish. In some circumstances, water can also strip additives from the oil through water washing or hydrolysis resulting in premature oil degradation.