If your cat all of a sudden starts "playing" with his water dish and splash water around, you need to take it seriously. If your cat has never displayed this trait before, or is older, there's a good chance your cat has a problem, and should be taken to the Vet to get a blood test and urine test, especially if your cat is drinking lots of water and urinating a lot.
Your cat is likely playing with his water and drinking a lot because he is dehydrated and may have Chronic Kidney Disease and / or Diabetes. If he's lost weight and acting strange, are all tell tale signs of the disease. Take your cat to the vet and get him check out, and have him get an IV of fluids.