Drinking a whole kilo of creatine dissolved in water in a sitting might be too much.
If you mean how much is enough before you're just wasting it, I would say 5g is about enough. I think this dose is supposed to give you enough and a little more just in case.
Now, bear in mind if you're a huge beef and salmon eater, you might be getting enough in your diet. One pound of beef can supply 2g creatine, and 1lb of salmon can supply 4g creatine. I eat about 1lb of beef and 0.5lb of salmon daily, so I get around 4g like that. I know others who eat twice as much of the same meat, easily, than I do, so their needs are covered.