A 20-year-old woman is in Waikato Hospital after she fell four metres from a water tower in Waikato today, injuring her neck, back and chest.

The woman - who climbed the tower every day to backflush the tank at her home in Tahuna, 26km southwest of Paeroa - lost her footing and slipped, a Westpac Waikato Air Ambulance spokesman said.

According to witnesses she slammed into the structure at least twice as she fell, he said.

She was treated at the scene then flown to Waikato Hospital.