How to Prune water canna?
Deadhead spent flowers to promote continual flowering, leave to die down in autumn

water canna · Canna 'Taney'
In summer, water cannas (often bred from Canna glauca) can be placed in containers in ponds with no more than 15cm (6in) of water over the roots. They are also suitable for well-watered borders or conservatories where potted plants can be stood in deep saucers of water. Before autumn frosts, bring plants from outdoors into a frost-free greenhouse or conservatory. Keep the pots moist but not saturated. In April, increase temperatures and plant the sprouted plants out in late May when the risk of frost has passed. See further canna cultivation advice
Deadhead spent flowers to promote continual flowering, leave to die down in autumn