It depends on what your understanding of a water ride is.
An old school triple drop log flume probably would be past its sell by date now, something a little more innovative wouldn't be. Take stormforce 10 at Drayton Manor for example, something along those lines would be great, arguably with a bit more theming.
It doesn't even have to get you drenched as others have pointed out we're not in Florida and it can make the day a little uncomfortable.
For me I love water rides, ideally one with a strong theme, I think Alton need more than just the rapids personally and I'd much rather see that than another coaster which in my opinion isn't required, although I accept this appears to be more family orientated.