For a start, you can hear all the noise all the time – aqua aerobics music, children squealing, splashing - and not just snatches between your own burbled breathing.
You can also see much more than just the unending line on the bottom of the pool.
As a workout, it definitely takes more energy than ordinary walking. The water provides resistance so that your arms get exercised as well as your legs. And, as with land, if you run, your burn rate increases.
For half an hour, I walked and jogged up and down the pool. In order to exercise a greater range of muscles, I did some laps forwards, some backwards and some sideways.
I found the silly walks embarrassing despite being largely in the company of lap swimmers (who couldn't see me), children (who didn't care), and other walkers (who looked equally odd).
Many, but not all, of my fellow pool walkers were women of a certain age, who chatted as they walked.
Pool walking is a relatively low impact workout. Even when jogging, I didn't experience the boob jolting that would have happened on land. That said, the sensation of my stomach fat rippling through the water was deeply disturbing.
Despite having more to see and hear than when swimming, I found pool walking more boring. It would be more fun if I'd had an exercise buddy to chat to. It would also be a good way to exercise in a home pool too small for swimming laps.
As the clock at last ticked up my half hour, I emerged from the pool feeling I'd had a decent workout – without so much as getting my hair wet.