March 2005

Vol. 20, No. 3     What's this?

Why Do A Freshwater Rinse?

from the March, 2005 issue of Undercurrent  

Anything doused in salt water retains a good bit of that salt when it dries. Salt cakes on the material, much as grains of salt in a saltshaker clump together in humid weather, and when the water evaporates, the salt crystallizes, with ions of sodium and chlorine arranging themselves in a tight geometric pattern. One saving grace is that, just like grains of salt in a saltshaker, in humid weather the crystals on your gear can remain loose for a day or two before they become unshakeable.

The buildup can be sneaky, perhaps scarcely noticeable over a week’s worth of diving. If left unrinsed, however, the crystals grow over time, and pressure forces them against the surface they’re lodged on till they begin to slowly cut into it. The result? Well, nothing, at first. Because the pro cess is slow, the effects of salt buildup aren’t dramatic until that awful moment when you discover the damage done. As salt buildup slowly cuts into parts like O-rings, their surfaces begin to develop tiny cracks that make them rougher. The rings also lose some of their flexibility, and they no longer fill the openings they were designed to fill. Salt buildup also does a number on metallic sealing surfaces.

So, while it’s still important to keep your dive equip ment freshwater rinsed, there’s no reason to panic if the day boat lacks an onboard rinse tank. You will have a day or two before the crystals begin to form, so it’s safe to wait till you’re back onshore.