You're looking at a luxury watch. The spec sheet says "300m water resistant" or "10 ATM." You nod as if you understand, then wonder: does this mean I can shower with it? Jump in a pool? Dive to 300 meters?
Water resistance is one of the most misunderstood watch specifications. Let's decode it.
Understanding ATM vs Meters
Water resistance is measured in two ways: ATM (atmospheres) and meters of depth. They're equivalent but represent different real-world scenarios.
ATM to meter conversion:
- 3 ATM = 30 metres
- 5 ATM = 50 metres
- 10 ATM = 100 metres
- 20 ATM = 200 metres
- 30 ATM = 300 metres
A watch with 10 ATM rating is 100 metres water resistant. These are equivalent measurements; manufacturers use both depending on region and convention.
How Water Resistance Is Tested
Luxury watch manufacturers test water resistance in a controlled lab setting. The watch is submerged to a specific depth in still, distilled water at rest—no movement, no pressure, no temperature changes.
This is crucial: lab testing ≠real-world use.
In the real world, your wrist moves constantly, temperature fluctuates, freshwater and saltwater have different properties, and water pressure changes. A 100m rated watch is not necessarily safe for 100m of diving.
The Rating Scale: What Each Level Actually Means
3 ATM (30m)
Real-world: Splash resistance only. Safe for accidental water exposure.
What's safe:
- Washing hands
- Light rain
- Splashes while washing dishes
What's NOT safe:
- Showers
- Swimming
- Any intentional water exposure
Common on: Dress watches, vintage pieces, delicate designs not meant for water sports.
5 ATM (50m)
Real-world: Light water resistance. Safe for snorkeling and casual swimming.
What's safe:
- Showers (if you're careful not to submerge)
- Swimming in a pool
- Snorkeling (brief submersion)
- Light splashing
What's NOT safe:
- Diving
- Water sports (surfing, water skiing)
- Prolonged submersion
Important: Even at 5 ATM, hot water from showers stresses the seals. Minimize shower wear if possible.
Common on: Most casual watches, some sports watches.
10 ATM (100m)
Real-world: Sports-level water resistance. Safe for swimming, snorkeling, and casual water sports.
What's safe:
- Showers (regular water pressure)
- Swimming and pool diving
- Snorkeling
- Water sports (non-professional)
- Jet skiing
- Casual diving (brief, shallow)
What's NOT safe:
- Professional or deep diving
- Saturation diving
- Extreme water sports (white-water rafting at high levels)
The Steinhart Sweet Spot: Many Steinhart watches are rated 10 ATM (100m). This is the practical choice for daily wear with regular water exposure. It covers 99% of real-world water activities for non-divers.
Common on: Dive-inspired watches, sports watches, active lifestyle watches.
20 ATM (200m)
Real-world: Serious water resistance. Safe for diving to moderate depths.
What's safe:
- Everything up to 10 ATM
- Recreational diving to 40 meters
- Professional snorkeling
- Intensive water sports
- Saturation diving (with reinforced seals)
What's NOT safe:
- Deep technical diving beyond 40 meters
- Decompression diving
- Commercial diving
Common on: Professional-grade dive watches, specialized sports watches.
30 ATM (300m)
Real-world: Professional dive watch rating. Safe for deep diving.
What's safe:
- Everything at lower ratings
- Recreational diving to 100+ meters
- Technical diving
- Professional diving (with proper seals)
- Commercial diving
Important: Even at 300m, a dive watch should only be used for diving if it's specifically designed for diving (meaning robust case, screw-down crown, helium escape valve for saturation diving).
Common on: Professional dive watches (Rolex Submariner, Steinhart Ocean One, TAG Heuer Aquaracer).
Beyond Numbers: Features That Matter
Water resistance rating tells part of the story. Real water protection depends on several features.
Screw-Down Crown
A screw-down crown (the knob you use to set the watch) adds a secondary seal. When screwed down, it prevents water from entering through the crown stem—a common failure point.
Why it matters: Even a 10 ATM watch with a screw-down crown is more reliable in water than a 20 ATM watch with a regular crown.
Steinhart watches: Many Steinhart models feature screw-down crowns, adding security for water exposure.
Gaskets and Seals
O-rings or gaskets at pressure points (crown, case back, crown guard) prevent water ingress.
Over time, gaskets degrade. A watch that was water-resistant 10 years ago may not be today—not because the rating changed, but because seals have degraded.
Maintenance: Have your watch serviced every 5–7 years. Service includes gasket replacement, which restores water resistance.
Case Back Type
Solid case back: Better for water resistance. The entire back seals the movement.
Transparent/crystal case back: Exposes a small window. Some transparent backs have adequate sealing; others don't. A transparent back watch generally has a lower effective water resistance than its rating suggests.
Helium Escape Valve
Used on dive watches for saturation diving (where divers spend days underwater). The valve lets helium gas escape during decompression, preventing case damage.
Not needed for recreational diving, but it's a sign of a professional-grade dive watch.
Real-World Water Exposure: The Rules
Freshwater vs Saltwater
Freshwater (pools, lakes, showers) is less harsh than saltwater.
Saltwater (ocean, salt spray) is corrosive. Salt deposits can damage seals and cause premature aging.
Rule: After saltwater exposure, rinse the watch thoroughly with freshwater and dry it immediately.
Temperature Matters
Hot water weakens gaskets. Cold water is gentler.
Avoid: Showering with a watch (heat), hot tubs, saunas, or steam rooms unless the watch is rated 10 ATM or higher.
Safer: Cool or lukewarm showers, and minimize even those.
Pressure During Activity
A 10 ATM watch is fine for swimming at the surface. But if you're diving, the pressure increases with depth. A wave crashing over you while you're snorkeling creates momentary pressure spikes.
Real-world lesson: A 10 ATM watch is safe for recreational activities at the surface. For diving, step up to 20 ATM or higher.
Regular Maintenance
Gaskets deteriorate over time. A five-year-old watch's water resistance may be compromised even if it was rated 10 ATM when new.
Maintenance interval: Every 5–7 years, have the watch serviced. Service includes:
- Gasket inspection and replacement
- Case pressure testing (to verify the rating still holds)
- Movement cleaning and oiling
Cost: Approximately R1,500–R3,000 depending on the watch.
Result: Your watch's water resistance is restored.
Dive Watches: What Makes Them Special
A true dive watch isn't just water-resistant—it's designed for diving.
Characteristics of a Dive Watch
- Minimum 30m (3 ATM) water resistance (professional dives require 100m minimum)
- Unidirectional rotating bezel: Prevents accidental adjustment during a dive. If bumped, it only rotates in one direction—increasing the safety margin.
- Large, readable numbers: Underwater, visibility is poor. Large numerals matter.
- Luminous markers: For low-light diving.
- Thick, durable case: Withstands pressure and impacts.
- Screw-down crown: Prevents water ingress.
- Robust bracelet or strap: Designed for durability, not delicacy.
Steinhart Dive Watches
Steinhart is renowned for dive watches, especially the Ocean One series. These watches feature:
- 300m water resistance
- Screw-down crown
- Unidirectional bezel
- Luminous dial and markers
- Professional-grade movement
These aren't watches that happen to be water-resistant. They're built for diving.
Professional Diving: When You Need Real Dive Certification
If you're planning to dive professionally or at depths beyond 40 meters, your watch needs to be up to the task.
Requirements:
- At least 200m (20 ATM) water resistance
- Screw-down crown
- Regular professional servicing
- Helium escape valve (for saturation diving)
- Professional certification (your dive certification + watch certification)
Saturation Diving
If you're doing saturation diving (staying underwater for extended periods, requiring decompression), your watch must be specifically rated and serviced for it. This is rare and professional-level.
Common Misunderstandings
"My watch is rated 100m, so I can dive to 100 meters."
Reality: No. Lab testing at rest is not equivalent to diving under pressure. A 100m watch is safe for recreational diving to about 40 meters. For deeper dives, get a watch rated 200m+ with proper dive features.
"If I don't submerge the watch, it's fine."
Reality: Showers subject the watch to pressure changes and temperature changes that stress seals. Even 5 ATM watches shouldn't be showered with regularly. Be conservative.
"Water resistance lasts forever."
Reality: Seals degrade over time. A watch loses water resistance if not serviced. Have it checked every 5–7 years.
"Saltwater is the same as freshwater."
Reality: Saltwater is corrosive and damages seals faster. After saltwater exposure, rinse and dry immediately.
"A watch with a transparent case back is less water-resistant."
Reality: Not necessarily. But transparent case backs do have a small window that's a potential weak point. Some are sealed excellently; others aren't.
Care and Maintenance for Water-Resistant Watches
After Water Exposure
- Freshwater: Rinse with distilled water if exposed to dust or sediment
- Saltwater: Rinse immediately with fresh water, then dry
- Chlorinated water: Rinse with fresh water (chlorine damages gaskets)
Regular Maintenance
- Service every 5–7 years
- Replace gaskets during service
- Pressure-test to verify water resistance
- Have the movement cleaned and oiled
Storage
- Store in a dry place
- Avoid temperature extremes
- If not wearing for extended periods, wind occasionally to keep the movement lubricated
Should You Get Your Watch Water-Tested?
Yes, if:
- You've had the watch for more than 5 years
- You've exposed it to saltwater
- You're planning to dive or do water sports
- You want to verify a used watch's water resistance
What's involved:
- The watch is placed in a pressurized chamber
- Pressure equivalent to the rated depth is applied
- If water enters, the test fails (and you know servicing is needed)
Cost: Approximately R300–R600.
Result: Peace of mind. You know whether the watch is safe for your planned activities.
Frequently Asked Questions
Q: Can I shower with my Steinhart watch?
A: If it's rated 10 ATM (100m) or higher, yes. But minimize it. The repeated temperature changes and pressure stress the seals. Occasional showers are fine; daily showers will shorten gasket life. Don't do it with a 5 ATM watch.
Q: Is my watch still water-resistant after 10 years?
A: Probably not at its original rating. Seals degrade. Have it serviced and pressure-tested. Service will restore water resistance.
Q: I accidentally submerged my 5 ATM watch. Is it ruined?
A: Probably not. Brief accidental submersion in a pool is usually survivable. But monitor it for fogging inside the crystal (sign of water ingress). If you see fog, get it serviced immediately.
Q: Can I snorkel with a 10 ATM watch?
A: Yes. Snorkeling at the surface (or near-surface) is safe with 10 ATM. For deeper diving or extended submersion, step up to 20 ATM or higher.
Q: Do I need a dive computer watch if I'm diving?
A: No. A dive watch is distinct from a dive computer. A dive watch is water-resistant and durable; a dive computer tracks depth, time, decompression stops, etc. For recreational diving, a dive computer is recommended. For casual snorkeling, a dive watch is sufficient.
Q: What's the difference between a dive watch and a sports watch?
A: A dive watch is optimized for underwater use (strong seals, readable underwater, durable). A sports watch is optimized for athletic activities (sweat resistance, durability, readable). A watch can be both, but they're different categories.
Q: My watch has a helium escape valve. What does it do?
A: It lets helium gas escape during decompression in saturation diving. If you're not doing saturation diving, you don't need it—it's an advanced feature.
Q: How often should I service my dive watch?
A: Every 5–7 years for regular use. If you dive professionally or regularly expose it to saltwater, every 3–5 years.
The Takeaway
Water resistance is about fit for purpose.
- A 5 ATM watch is for splash protection and light water contact
- A 10 ATM watch is for swimming and recreational water sports
- A 20 ATM watch is for serious water sports and recreational diving
- A 30 ATM watch with dive features is for professional diving
Know your watch's rating, respect its limits, and maintain it properly.
At Pura, we specialize in Steinhart dive watches—some of the finest water-resistant watches available. If you're considering a watch for water activities, we can explain the specs and help you find the right piece.
Questions about a specific watch's water resistance? Bring it in, and we'll discuss what it's actually safe for.