Quick Answer: Most water inside a sealed cache is condensation, not leakage. Warm humid air trapped inside during the day cools overnight, and moisture condenses on the container walls. Late summer has the largest day-to-night temperature swing of the year combined with high humidity, which is why caches that were dry all spring turn wet in August. The fix is a desiccant pack, a zip bag around the log, and choosing a container with a real gasket.

It is a genuinely annoying discovery. The seal looks intact, the container is undamaged, and the log inside is a wet brick that cannot be signed.

Why does a sealed container get wet inside?

Because you sealed air in it, and air carries water.

Warm air holds more moisture than cool air. When a cache is closed on a warm humid afternoon, the trapped air carries a substantial amount of water vapor. As temperature drops overnight, the air’s capacity falls and the excess condenses on the inside surfaces.

The container is the coldest thing in the system. Plastic and metal lose heat faster than the air inside, so condensation forms preferentially on the walls and lid, then runs down onto the log.

Every open and close resets it. Each finder introduces a fresh charge of humid air. A popular cache in humid weather gets re-loaded with moisture several times a week, which is why busy caches are often the wettest ones.

Late summer maximizes both variables. Humidity is still high, and the day-to-night temperature swing is at its largest of the year as nights lengthen. A 15-degree overnight drop with humid daytime air is the ideal condensation machine.

Which is why a dry spring proves nothing. Cool, dry spring air condenses far less. The same container in the same spot behaves completely differently in August.

How do you tell condensation from a leak?

The pattern of the water tells you, and it takes ten seconds to read.

Condensation appears as even droplets on the lid and upper walls. It is distributed, fine, and heaviest at the top - because that is where the coldest surface and the rising moist air meet.

A leak collects at the bottom. Standing water in the base with dry upper surfaces means water entered from outside, usually through a failed gasket, a hairline crack, or a threaded lid that was not fully closed.

Check the gasket by feel. A good gasket is soft and springs back. A gasket that is hard, flattened, or cracked has failed, and this is the most common physical failure on outdoor containers after a couple of seasons.

Look at the placement. A container sitting where water runs, under a drip line, or in a hollow that pools will take on water regardless of how good the seal is. Placement causes more wet caches than container quality does.

And check for a cross-threaded lid. Screw-top containers close crookedly very easily when someone is in a hurry, and a lid that is one thread off looks closed and seals nothing.

5 Mistakes Everyone Makes With Cache Containers

1. Using a food container as a waterproof one. Most kitchen storage containers seal against spills, not against a season outdoors. They lack a true compression gasket and the plastic becomes brittle with UV exposure. Ammo cans and purpose-made outdoor containers are a different category of product.

2. Putting the log in loose. Even a perfect container will eventually see moisture. A log inside a small zip bag survives condensation indefinitely, and the bag costs nothing.

3. Skipping the desiccant. A silica gel pack absorbs the moisture that gets trapped at each closing. It is the single highest-value item you can add to a cache and it fits anywhere. Replace it once or twice a year.

4. Closing it on a humid afternoon. If you have a choice, close a cache in the coolest, driest part of the day. Sealing at 3pm in August traps the worst possible air.

5. Not checking your own caches after a season change. Late August is the point at which conditions shift. A maintenance visit now catches the wet log before six finders report it, and it is the difference between a cache that stays active and one that gets archived.

What actually keeps a cache dry?

A layered approach, because no single measure holds through a full year.

Start with a real gasket container. Ammo cans, purpose-built cache containers, and screw-top jars with a compressible O-ring all work. The gasket is the component that matters - everything else is packaging.

Add silica gel. A few grams inside handles the residual humidity from repeated opening. Rechargeable packs that change color when saturated are ideal because they tell you when to act.

Bag the log separately. A small zip bag inside the container is a second seal around the only thing that genuinely cannot be replaced without a maintenance visit.

Place it above the water path. Slightly elevated, out of a hollow, not under a drip line from a rock or branch, and not in the lowest point of a wall cavity. Placement is free and it outperforms every other measure.

Orient the lid so it does not face up into rain. A container on its side with the opening horizontal takes on far less water through a marginal seal than one lying lid-up.

And check it seasonally. Two maintenance visits a year - one in late summer, one in early spring - catch nearly every problem before finders do.

FAQ: Wet Cache Questions, Answered

Are ammo cans really the best containers?

They are among the most reliable for medium and large caches: a genuine rubber gasket, rigid steel, and a latch that applies real compression. Downsides are weight, rust at the seams over years, and the fact that they can alarm passers-by in urban settings.

Does drilling a drain hole help?

It lets water out, but it also lets humid air, insects, and slugs in continuously. Generally it is a last resort for a container that cannot be replaced, not a design choice.

How often should silica gel be replaced?

Twice a year for a moderately visited cache in a humid climate. Color-indicating packs remove the guesswork - when the indicator changes, it is saturated and doing nothing.

Why is my urban cache wetter than my woodland one?

Often temperature swing. Urban caches tucked against metal or stone experience larger daily temperature changes than shaded woodland ones, and larger swings mean more condensation cycles.

TL;DR:

• Most cache water is condensation from trapped humid air, not rain getting in.
• Late summer combines high humidity and the largest day-night temperature swing of the year.
• Droplets on the lid mean condensation; standing water in the base means a leak or bad placement.
• Gasket container plus silica gel plus a bagged log solves it - and placement above the water path is free.

The reason to do a maintenance round now rather than in October is that the wet-log reports are about to start arriving, and every one of them slightly reduces the chance a finder logs the cache at all. Ten minutes, a fresh log in a bag, and a new desiccant pack keeps a cache in service through the whole wet half of the year.