This is one of Suffolk's great recreation areas. The Anglian Water Authority have done a good job in making this a relaxation/sporting area. There is a footpath and cycle route around the 8 mile perimeter, just a reminder that in prolonged heavy rain there are one or two places that do get quite muddy.
We walked around the 'Waters' a few years ago now and allowed 3 hours and it took just over that with a tea break at the sailing club restaurant. There are one or two hilly places and not too many seats!
Sailing, fishing [in selected places], windsailing, walking, cycle hire, special events, two cafes and two main car parks, bird watching hide and a shorter 3 or 4 mile walk around the Lemons Hill section of the reservoir which also acts as a nature/bird reserve. This all makes up a good day out. £3 a day parking at the Main Car Park, free at the other locations eg Lemons Hill Bridge, Tattingstone