Water monitor comparison
Spa and pool water monitors, compared honestly.
We sell E.W.A., so this is not unbiased. What we have tried to do is state each product's subscription status and price plainly, and be upfront about the gap in this category: Sutro, a subscription-based monitor, was reported to have shut down in October 2025.
What each one measures, and what it costs
Prices below are publicly listed by each manufacturer as of this writing, not independently verified in a lab. Listed prices and terms change, verify current pricing directly with the manufacturer before buying.
| Monitor | Measures | Ongoing cost | Price |
|---|---|---|---|
| E.W.A. | pH, ORP sanitizer, temperature | None, ever | EUR 695, one time |
| iopool EcO | pH, chlorine, temperature | None | EUR 279, publicly listed |
| Ondilo ICO | pH, ORP, temperature, salt | None confirmed | ~USD 449, publicly listed |
| Blue Connect (Blueriiot) | pH, chlorine/salt, temperature | None confirmed | EUR 425 incl. VAT, publicly listed |
| WaterGuru SENSE 3 | pH, sanitizer, alkalinity, cyanuric acid | Replacement cartridges, ~USD 69 | Unit price not public |
| Sutro | Was pH, chlorine, alkalinity | Was USD 29-39/month | Discontinued Oct 2025 |
The Sutro lesson
Sutro was publicly listed at around USD 499 plus a USD 29-39 monthly subscription. It was reported to have shut down in October 2025, with its devices no longer working, leaving owners with hardware they had paid for and could no longer use. Verify current status directly if you already own one. It is the clearest recent example in this category of what a subscription dependency costs you when the company behind it stops.
E.W.A. has no subscription of any kind, for exactly that reason: a device that reads your water should keep working for as long as the hardware does.
Why measurement depth matters more than the spec sheet
Most water monitors list pH and a sanitizer reading. The meaningful difference is how the sanitizer reading is taken. E.W.A. reads ORP (oxidation reduction potential), the actual killing power of the sanitizer in your water, not just how much of it is present as a ppm number. A pool or spa can show a normal chlorine ppm and still be unsafe if the pH is off, which a ppm-only reading will not catch.
Common questions
What happened to Sutro?
Sutro, a subscription-based water sensor, was reported to have shut down in October 2025, with its devices no longer working. Verify current status directly if you own one. It is a cautionary example of what happens when a physical device depends on an ongoing subscription to keep functioning, one reason E.W.A. has no subscription of any kind.
Is E.W.A. cheaper than other water monitors?
E.W.A. is EUR 695 one time, with no subscription. iopool EcO is publicly listed lower at EUR 279 with no subscription either. Ondilo ICO and Blue Connect sit closer to E.W.A. on price. WaterGuru does not publish a unit price but sells replacement cartridges. Price alone does not tell the whole story, what each device measures and whether it has an ongoing cost matters more over several years.
Why does E.W.A. measure ORP instead of just chlorine ppm?
ORP (oxidation reduction potential) measures how strongly the sanitizer is actually working, not just how much is present. A chlorine ppm reading can look fine while pH is off and the water is genuinely unsafe. ORP catches that, which is why E.W.A. reads it rather than ppm alone.
Does E.W.A. work for pools as well as spas?
Yes. The same core numbers (pH, sanitizer, temperature) balance a pool as well as a spa or hot tub. E.W.A. reads the water itself, not spa-specific equipment, so it applies to both.
Do any of these have a subscription I should watch out for?
Sutro required one and no longer exists. WaterGuru does not charge a subscription but does sell replacement cartridges as a recurring cost. iopool, Ondilo and Blue Connect are not publicly confirmed to charge one. Always verify current pricing and terms directly with each manufacturer before buying, listed prices change.
Stop guessing at your water.
E.W.A. reads pH, sanitizer and temperature in real time and tells you exactly what to add. One time price, no subscription, ever.