The Pentax PCF WPII binoculars can handle 1 meter depth of water, or 3.28 feet.
Ingress Protection (IP) is the name given in industry to the designs solutions to avoid penetration of dust and water in all sorts of equipments.
IP was first standardized by the International Electrotechnical Comission (IEC) with the IEC 60529 being the lastest edition of the standard, also adopted in Europe as EN 60529. Both standards have been used by different manufacturers to design their products against dust and water penetration, in several areas of industry.
Japanese use its own industry standard JIS C 0920 (last edition released in 2003) and this is the standard used by Nikon and Pentax to design their waterproof products. JIS C 0920 is similar with the IEC 60529. I could not find a comparable table between the two, other than in japanese language.
US industry uses mainly NEMA standard number 250, wich is somewhat similar to IEC 60529, but allows for some other conditions and installations types. Nema is a standard covering enclosures IP in different conditions and with different installations and IEC 60529 covers the parameters for IP classification and establishes levels of protection.
You will also find IK, wich is a group of parameters to establish mechanical resistance.
Immersion in water for 30 minutes, at a deep of 1 meter is equivalent to IP 67 in the IEC standard, meaning the seals will avoid penetration during the maximum given time of 30 minutes at a pressure of 0,1Kgf/cm2 (1,422 psi), but this will not be completely watertight, neither hermetic and one should expected to see the watertightness break after that amount of time or at a higher depth. If the pressure increases slightly, the amount of time will decrease radically and at higher depths, the pressure will be enough to penetrate the seals of the binoculars in the first few seconds. It is all a matter of pressure and this is most important than the time under water. If you drop your binoculars in 5 or 10 meters of water they will probably suffer penetration during the first seconds, even if they are able to sustain more time at smaller depths.
Some of you may have read before about not putting binoculars under a tap with running water. This is funny because the tap is not submerged and there should not be penetration, rigth? Wrong! Tap water sometimes runs strong and actually has a lot of pressure. If the pressure goes above the value designed by the manufacturer, you will have a break of the pressure seal and penetration inside the binoculars.
Some binocular manufacturers seem to have their own rules and I have been reading several different values in specifications.
Make shure you see some standard close to the waterproofing values given by the manufacturers. If you need watertightness as a routine feature make shure they are the highest possible numbers. I have seen everything from 1 to 30 minutes and from 1 to 5 meters waterproof levels, outside the standards and without relating directly to the original IEC or JIS standard.
There is no complete hermetic binocular out there and I avoid contact with water, even with waterproof gear. Salt water specially.
H2O contains minerals and salts, some of them with acidic PH and one never knows what it will do to the metallic parts of the binoculars and, (much worse) what it will do to coatings.