It can take some time. We started solids at 6.5m (did purees first). One of my boys took to them right away but the other hated solids for about the first 3-4 weeks so we had to take it slowly with him. Does your LO still have the tongue-thrust reflex? If so, you might want to hold off for now and try again in a few weeks. Also, when you say watered down, are you mixing it with water or with breastmilk or formula? If water, I would try using breastmilk or formula instead.
I would wait a few weeks and try again. And honestly, we never did plain rice cereal. It can cause constipation and doesn't offer much nutritionally. We started with bananas and avocados.
Re: Question about eating rice cereal?