Water Hyacinths should be treated as an annual plant in this country. They reproduce rapidly. Each plant can be expected to produce many more plants by offsets throughout the summer. They are useful in providing extra shade and shelter for small life forms and remove nutrients from the water with their feathery roots. Suitable for any depth of water over 3 inches 7.5cm.
Generally they are unlikely to flower in the U.K.climate. But when produced are pale lilac and I have had up to three flowers from one plant.
Sold on the nursery for £1.35 each or 4 or more £1.25 each. For sending they are in fours unless you want one or two as part of an order with more plants due to the economics of posting them.