It's surely a lot better to ask the question, than assume it's ok.
There's such a range of possible situations here - on one extreme, a busy adult size (and depth) pool, with sunloungers spread about, with the OP playing on lying down and sunbathing. No responsible parent would think that was ok.
On the other end, you've got a toddler size paddling pool in a garden with a sunlounger right next to it. Most people (IMO) would be fine with that - the adults often wouldn't even fit!
A couple of months ago, I remember a post on here av.out what age children can be unsupervised in the bath. Most people were ok with popping out, being just nearby/next room by 4ish. This isn't the thread but it's in the same topic (stupid search function couldnt find the recent one)
www.mumsnet.com/talk/_chat/3380704-what-age-did-you-leave-your-child-unsupervised-in-the-bath
It feels contradictory that on this thread, people are clear that drowning takes seconds, a couple of inches of water, and even looking at your phone standing next to the water is a risk, when at the same age people are routinely apparently leaving their kids alone in the bath, for a few minutes at a time.
I've never been to a splash pad etc, where parents have stayed in arms reach, except for very young walkers. In my local splash pad, there's an area with a toddler pool, very shallow, but still a pool. Parents certainly weren't staying within arms reach of under 5's (I was staying with mine but was the only one, except for under 2's. So I can understand why this question arises.