If you’re comparing the Coway Bidetmega 400S vs 400, you’ve found two of the most talked-about bidet seats from this brand — but one is the clear winner for new buyers today.
This head-to-head breakdown covers every key difference so you can decide which Coway Bidetmega is right for you.
| Feature | Coway Bidetmega 400S | Coway Bidetmega 400 |
|---|---|---|
| Image |  |
[No longer available] |
| Dimensions (L x W x H) | 20.94″ x 14.96″ x 5.28″ | 21.2″ x 19.54″ x 5.31″ |
| Water Heating | Tankless instant heat | Tankless instant heat |
| Wash Technology | i-wave: 3-stage course or 1-stage + Move/Wide/Air+ | i-wave: 4-stage wash process |
| Hygiene System | Triple Hygiene Care: WaterShield mist + UV nozzle light + auto-clean nozzle | 3-stage: water path + nozzle + toilet bowl |
| Seat Temperature | 4 settings with overheat protection | 3 settings |
| Waterproof Rating | IPX4 | IPX5 |
| User Profiles / Child Mode | 2 user profiles + child mode | Child mode (Braille remote) |
| Buy Now |  |
Discontinued — not available |
1. Coway Bidetmega 400S
The Bidetmega 400S is Coway’s current flagship bidet seat, launched in early 2025 as the direct successor to the original 400.
It brings a meaningful set of upgrades in hygiene technology and comfort customization while keeping the core features that made the 400 so popular among bidet enthusiasts.
If you’re looking for one of the best bidets for existing toilets, the 400S sits firmly near the top of that list.
Features
- Tankless instant water heating with no wait time or interruption
- Updated i-wave cleaning: 3-stage course wash or 1-stage general wash, customizable with Move, Wide, and Air+ spray modes
- Triple Hygiene Care: WaterShield mist (automatic bowl protection before and after use), auto-cleaning stainless steel nozzle, and UV nozzle sterilization light
- 4 heated seat temperature settings with overheat protection
- 4 adjustable dryer temperature settings
- 2 programmable user profiles + dedicated child mode
- Soft-close lid, LED nightlight, wireless remote, eco mode
- IPX4 water resistance rating
- Available in round and elongated
Pros
- WaterShield bowl mist is a genuinely impressive hygiene upgrade
- UV nozzle sterilization adds peace of mind that most competing bidets don’t offer
- Air+ mode aerates the water stream for a gentler yet thorough clean
- Two user profiles make it easy for couples or family households to personalize settings
- Intuitive wireless remote with wall-mount or tabletop base
Cons
- IPX4 rating is slightly lower than the original 400’s IPX5
- Air dryer, while functional, could be stronger — a common observation across this product line
- Requires a nearby grounded electrical outlet
The 400S is the right seat if you want a fresh out-of-box bidet with the latest hygiene features and full manufacturer support — which makes it the smarter investment for most households.
Check its current price on Amazon
2. Coway Bidetmega 400 (Original)
The original Bidetmega 400 is the model that put Coway on the map in the U.S. bidet market, earning a loyal following for its reliable performance and comprehensive feature set at a competitive price point.
It was a serious mid-to-high-range option that competed well with other bidets for home use for several years.
Features
- Tankless instant water heating
- i-wave 4-stage wash process with Rear, Front (feminine), Active Move, and Soothing Wash modes
- 3-stage cleaning system covering water path, nozzle, and toilet bowl
- 3-level heated seat temperature
- Warm air dryer
- Child mode, ECO mode, LED nightlight
- Wireless remote with Braille buttons for accessibility
- IPX5 waterproof rating
- Available in round and elongated
Pros
- Proven, reliable performance over multiple years
- IPX5 rating is actually higher than the 400S — better water resistance
- Braille-marked remote is a thoughtful accessibility feature
- 3-stage cleaning care kept the water path and nozzle hygienic
Cons
- Discontinued — no longer available new on major retail platforms
- No WaterShield bowl mist or UV nozzle sterilization
- Only 3 seat temperature levels vs the 400S’s 4
- Fewer wash customization modes compared to the 400S
- No multi-user memory profiles
The 400 was a solid bidet in its time, but its discontinuation makes it a difficult choice — spare parts and warranty support are limited, and purchasing used units carries obvious risks.
Cleaning Technology: 400S Wins
Both models use Coway’s proprietary i-wave wash system, but the 400S pushes the technology further.
While the original 400 used a 4-stage wash process with preset modes, the 400S gives you more granular control — you can select a 3-stage course wash or a 1-stage general wash, then layer in Move (oscillating nozzle), Wide (dispersed spray for sensitive skin), and Air+ (bubble-infused stream for deeper clean).
More importantly, the 400S adds WaterShield mist and UV nozzle sterilization to its cleaning arsenal.
The original 400 cleaned the water path, nozzle, and bowl — solid for its time, but the 400S’s Triple Hygiene Care system is a meaningful step forward for anyone who prioritizes hygiene above all else.
Winner: Coway Bidetmega 400S
Comfort Features: 400S Wins
Both models deliver instant heated water, a heated seat, a warm air dryer, a nightlight, and child mode — the core comfort package you’d expect from a quality electric bidet seat.
The 400S goes further with two programmable user profiles, which are invaluable for households where more than one person has distinct preferences.
Seat temperature settings also increase from 3 levels on the 400 to 4 levels on the 400S, with added overheat protection for extra safety.
If you’re comparing comfort features across similarly priced options, you’ll find a detailed breakdown in our bidet toilet seat comparison chart.
Winner: Coway Bidetmega 400S
Water Resistance: Original 400 Wins
This is the one area where the original 400 technically outperforms its successor.
The Bidetmega 400 carries an IPX5 rating, meaning it can withstand low-pressure water jets from any direction — a slightly more rigorous standard than the 400S’s IPX4 rating, which covers sustained low-pressure water exposure.
In practice, neither rating makes a difference for normal bathroom use — a bidet seat is not going to get blasted with a hose.
But if waterproofing matters to you on a spec level, the 400 holds an edge.
Winner: Coway Bidetmega 400 (original)
Availability & Value: 400S Wins
The original 400 has been discontinued and is no longer sold new through major retailers.
That alone ends the debate for most buyers — you can’t easily buy the 400 new, and used units don’t come with warranty coverage or support.
The 400S is fully available, backed by Coway’s warranty, and priced competitively for its feature set.
If you’re shopping for a premium bidet that delivers long-term value, it also helps to know that bidets with dryers at this price tier consistently outperform cheaper models without them over the long run.
Winner: Coway Bidetmega 400S
Installation: Tie
Both models install the same way — remove your existing toilet seat, attach the bidet bracket, connect the T-valve to your water supply line, and plug into a grounded 120V outlet.
Most users complete the full setup in under an hour without professional help.
If you’re new to bidet seats, check out our guide on the differences between a bidet toilet vs bidet seat before deciding which type fits your bathroom best.
Winner: Tie
Verdict — Which One Should You Buy?
This comparison has a clear answer: buy the Coway Bidetmega 400S.
The original 400 was a great bidet, but it’s discontinued and no longer available new.
The 400S is the better product on nearly every dimension — improved hygiene technology, more wash customization, an extra seat temperature setting, dual user profiles, and the security of full manufacturer support.
Buy the Coway Bidetmega 400S if… you want the best current Coway bidet seat with Triple Hygiene Care, UV nozzle sterilization, and a WaterShield bowl mist that genuinely elevates your bathroom hygiene routine.
Consider used Coway Bidetmega 400 only if… you find a well-maintained unit at a price that’s too good to pass up and you’re comfortable without a warranty — but know that the 400S has more features and is a safer long-term purchase.
Check the current price of the Coway Bidetmega 400S on Amazon
Frequently Asked Questions
Is the Coway Bidetmega 400 still available?
No. The original Coway Bidetmega 400 has been discontinued and is no longer sold new on major retail platforms including its primary online retailer. The Bidetmega 400S is its direct replacement and is fully available today.
What are the biggest upgrades in the 400S vs the original 400?
The 400S adds WaterShield bowl mist, UV nozzle sterilization, Air+/Move/Wide spray modes, a fourth seat temperature level, dual user profiles, and a soft-close lid. These are meaningful upgrades, not just cosmetic changes.
Does the Coway Bidetmega 400S work with round toilets?
Yes. The 400S is available in both elongated and round versions. Make sure to select the correct bowl shape when purchasing. If you’re unsure about compatibility, our guide to bidets for existing toilets has helpful measuring tips.
How does the Coway 400S compare to other premium bidets?
The 400S competes well against other mid-to-high-end electric bidet seats in its price range. Its Triple Hygiene Care system — particularly the WaterShield mist and UV sterilization — is a standout differentiator. For a broader look at how it stacks up, our full bidet toilet seat comparison chart breaks down the top models side by side. You may also find it helpful to browse our best bidets under $500 roundup and our guide to the best bidets for seniors if accessibility and ease of use are priorities for you.
Conclusion
The Coway Bidetmega 400S vs 400 debate has a straightforward conclusion: the 400S is the better product and the only one you can actually buy new today.
The original 400 was a well-loved, capable bidet seat — but it’s been discontinued, and the 400S replaces it with genuine improvements across hygiene, comfort, and customization.
If you’re upgrading your bathroom hygiene routine and want a premium bidet that delivers every time you sit down, the 400S is the one to get.
And if you’re still exploring your options, take a look at our handheld bidet vs bidet seat guide to understand which style suits your lifestyle best before you commit.
Check the current price of the Coway Bidetmega 400S on Amazon
