You may know of the giant water lily, Victoria regia /amazonica. The remarkably rigid structure of the leaves with their upturned rims and interlaced ribs makes these stiff enough to support a child. They gave Paxton his idea for the iron framework of the Crystal Palace. Unfortunately apart from needing more than considerable warmth this plant requires more than a modest greenhouse- each leaf can be as large as a dining table. Still, you might be able to justify the extravagance by considering it a food crop- the seeds can be roasted and eaten.
Indeed it may be surprising but not only are most water lily seeds edible so also is almost every other part of some species or another. The roots of many are eaten, as are the flowers, seed capsules, stalks, tubers and seeds of others, though apparently not the leaves. It seems surprising we’ve never developed water lilies more as a vegetable harvest from otherwise unemployed areas of water. There are three major genus- Nelumbo, Nuphar and Nymphaea with the last providing the majority of the more ornamental water lilies widely available- mainly in red and pink variations although there are one or two blue and several white forms. As with most plants the best cultivars have to be propagated vegetatively to stay true so for these you need to buy small ones to start with. However the species can be grown from seed (indeed the Victoria is usually grown as an annual!) and this is not much more difficult than for most other tender plants, though you may need to slowly increase the depth of water for the seedlings.
To keep water lilies happy they need to be set at the right depth, most are best with about two foot or so of water though a few prefer less and some nearer three. Anyway you can grow many of the less vigorous ones in convenient containers such as plastic drums or even old baths. And although some require quite warm water most survive being outdoors in summer and can be moved out to decorate the patio. The key is to have the water level near the brim then the blooms and decorative leaves are more fully visible. Special plastic planting baskets are useful though terra cotta pots work well if big enough.
A soil based potting compost works best (peat or substitute ones are too light) and to stop this washing out add a topping of coarse gravel. There are not many pests or diseases commonly bothering water lilies -and even fewer pests if you keep a few fish in the water. However do not have fish needing an air pump or running water as water lilies much prefer still water to moving. With no pruning or much other care required these are relatively low maintenance plants giving years of pleasure. And one, Nymphaea alba, was once used in France to make a kind of beer- now you can’t do that with most other greenhouse subjects!