# Water Purifier Diary vs OtterBoard

The clearest difference is update cadence: OtterBoard at every 3 days against Water Purifier Diary's every 3 weeks. Water Purifier Diary's advantage is device support (3 vs 1) and iOS requirement (13.0 vs 17.0). On price, ads and in-app purchases there is nothing between them.

Both are free to download. Water Purifier Diary sells 2 in-app purchases, starting at $0.99 per month and OtterBoard sells 8 in-app purchases, starting at $5.99 per year. Whichever you choose, the download price is not the number that matters.

Water Purifier Diary ships an update every 3 weeks, OtterBoard every 3 days. The most recent releases landed on October 7, 2026 and October 29, 2026 respectively.

## The numbers

| Metric | Water Purifier Diary | OtterBoard |
| --- | --- | --- |
| Price | Free | Free |
| In-app purchases | Yes | Yes |
| Ads | Yes | Yes |
| Update frequency | Every 3 weeks | **Every 3 days** |
| Size | 41 MB | 227 MB |
| Requires iOS | **13.0** | 17.0 |
| Devices | **iPhone, iPad, iPod** | iPhone |
| Age rating | 4+ | 4+ |
| Developer | [HAO CHANG KUO](https://appshunter.io/developer/1735524069) | [One Eternal](https://appshunter.io/developer/6792182843) |

## What reviewers say

### Water Purifier Diary

[App page](https://appshunter.io/ios/app/water-purifier-diary/id6761051602)

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases (2)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Pro (Monthly) | $0.99 | per month |
| Pro (Yearly) | $8.99 | per year |


### OtterBoard

[App page](https://appshunter.io/ios/app/otterboard/id6803947273)

**Features:** iPhone Duo support

**In-app purchases (8)**

| Purchase | Price | Billing |
| --- | --- | --- |
| OtterBoard Pro Yearly | $5.99 | per year |
| 極光鍵盤主題 | $1.99 | one-time |
| 青苔螢火鍵盤主題 | $3.99 | one-time |
| 墨流鍵盤主題 | $4.99 | one-time |
| 夢幻泡泡鍵盤主題 | $5.99 | one-time |
| 機械 RGB 鍵盤主題 01 | $5.99 | one-time |
| 倉頡碼雨 Cangjie Rain 鍵盤主題 | $5.99 | one-time |
| OtterBoard Pro Lifetime | $14.99 | one-time |


## Frequently asked questions

### Is Water Purifier Diary free?

Water Purifier Diary is free to download, with in-app purchases available.

### Is OtterBoard free?

OtterBoard is free to download, with in-app purchases available.

### Do Water Purifier Diary or OtterBoard have ads?

Both Water Purifier Diary and OtterBoard show ads.

### Which is updated more often, Water Purifier Diary or OtterBoard?

Water Purifier Diary ships an update every 3 weeks, and OtterBoard every 3 days. Most recently, Water Purifier Diary was updated on October 7, 2026 and OtterBoard on October 29, 2026.

---

*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*