levadopa is absorbed in the duodenum - a little pouch that comes after the stomach.
assuming - fast absorption is good:
the duodenum is slowed down by cold and, to a lesser extent hot, liquids and food.
it is also slowed down by acid, protein and fat.
protein not only works against levadopa at the blood brain barrier but also in the duodenum. carbs are fastest.
therefore (or not!) its best to drink body temp water with levadopa rather than cold or hot, no orange juice or milk, especially straight from the fridge.http://gut.bmj.com/content/29/3/302.full.pdfhttp://www.aic.cuhk.edu.hk/web8/gastric_emptying.htm
keeping your duodenum happy might also help reduce the chances of dyskinesiahttp://www.neurology-apd.com/articles/why-should-levodopa-be-infused-duodenum
the last article also has some interesting ideas on why levadopa stops working eventually.