Just got a bowl for my future betta it has a 6 litre capacity and is quite a biggest bowl. My question is how far should a fill the water level up, because i read somewhere that betta's are good jumpers. The bowl also has a plastic hood but its not completely covered.

I will try and find a picture of the bowl i'm talking about.

http://www.seapets.co.uk/product-details/stkcode/120000.html

Its very similiar to this bowl in this link.

I've never had jumpers but I hear that a lot of people do. Leave about the water level about 1 inch down from the top. A betta will be discouraged from jumping. Since you have it down low I found it is fun to get fake plants that stick out the top. Kind of reminds me of mangrove forests.

Here are my bowls planted with plants that stick out and even hang over.

Sushi is right . An inch or two from the top will do. If you are still worried about him jumping you can always put a lace dollie over the top. It will let air in, look pretty and keep him from jumping. I mainly have trouble with Zeke wanting to jump when I net him for something. He always tries to jump out of the net. He has never tried to jump out of the tank .