Scholarly encyclopedias will provide background information and references as well to other useful resources.
Subject Encyclopedia Examples:
Water Encyclopedia (Wiley)
Treatise on Water Science (Elsevier)
Wikipedia
BEWARE: Can provide useful background information, but don't believe everything you read! Evaluate and verify.
Contentious Science Topics on Wikipedia Subject to Editing Mishchief by Meghan Rose, Science News [188;7, Oct. 3, 2015, p. 5.]