Fibreglass Tanks
Fibreglass tanks are quite rare today, but require a food-grade coating to be up to Australian standards for storing drinkable water.
Tanks made of fibreglass are often very stiff and rigid, but relatively thin and light making them quite brittle and prone to cracking. They also allow more light entry and often found in darker coloured to help reduce algae growth.
The quality of a fibreglass tank depends on its maker, so if for some reason you go with this material, just be sure to check the quality thoroughly.