from the equal website....
5. If water is inside a tire, does it have any effect on EQUAL, and if so, what is the effect?
EQUAL Tire Performance does NOT ABSORB water in any way.
Due to the fact that EQUAL is a plastic polymer granule, water or moisture will not change its composition.
Moisture that accumulates inside the tire will evaporate due to normal driving conditions and therefore is in contact with EQUAL for a very short time.
EQUAL, when in contact with large amounts of water, (to the point where it is actually floating freely), will do just that, float. This will interfere with the ability of EQUAL to optimize the given tire in the way that the tire dealer or fleet had intended when installing the product. Simply, this means that although EQUAL will never damage the tire in any way, if it is in contact with large amounts of water, it cannot perform its job. Again, it is important to reiterate, that in most cases, moisture will evaporate due to the heat build up in normal driving, and once the moisture has evaporated, EQUAL will perform as it originally did.
http://www.imiproducts.com/equal/faqs.aspx