Healthy waterlilies are very tough plants. They withstand rains, winds, droughts, hail storms, and neighborhood kids with sticks. And more importantly, pests usually ignore them. Thriving lilies grow fast and bloom well, with plenty of leaves and regular blooms. There are enough lily pads so that an occasional pest nibble can be trimmed away without making a dent in the appearance or health of the plant.
A healthy waterlily has good soil (not potting soil) in a suitably large container — 2 ½ gal or more. Lilies are hungry feeders and should be fertilized at least every growing season. A controlled-release fertilizer with micronutrients is ideal. Most lilies (especially tropicals) benefit from repotting every other year. The type of waterlily and the climate zone obviously affect how fast it grows, how large it gets, how much food it needs and how often it should be repotted or divided.
The bottom line is that healthy waterlilies are more attractive, have larger and more frequent blooms and are less likely to be attacked by pests or diseases.