Margaret Beckett, Secretary of State for the environment, food and rural affairs, presented the award to environmental co-ordinator Emma Goodard (pictured) at the Lincoln Centre, Lincoln's Inn Field.
The company received the award for its outstanding environmental work in creating a variety of habitats on its land, including hedges, woodland and reedbeds.
Its work includes managing 17 Sites of Special Scientific Interest, a National Nature Reserve, two Local Nature Reserves and numerous Areas of Outstanding Natural Beauty.
The awards assessor said: "This is a small water company punching above its weight.
"There is an innovative and creative programme — excellent value for money."