Nah, all this means is water in the actual lake system. So if you jumped into rumbas water, it's not treated. Best of luck, it might be awful.
Water pumped through the features will be from tap water though. Unless they have a filtered system, of which I highly doubt they do considering they're all hose pipes. So taps for that.
Water into lakewise, it's a man made lake so doesn't matter. But the water they chuck on you I highly doubt is chlorinated anyway (other than chlorine in the local mains) but either way it wouldn't matter.