Depending on the species, fertilization can occur internally or externally. Water aids the fertilization of some organisms because organisms that reproduce externally need water for fertilization to occur.
In humans internal fertilization is found and it occurs during after intercourse when male ejaculated its sperm in female vagina and when one sperm cell fuse with ovum of female then fertilization occur and which produce an egg cell.
Internal fertilization is a form of animal fertilization of an egg by sperm within the body of an inseminated animal, whether female or hermaphroditic. This is distinct from external fertilization, where the union of the ova and spermatozoa occur outside of the organism.
internal fertilization is, by definition advantageous because it is natural. In Vitro fertilization is advantageous for those who cannot have children naturally because it allows the miracle of birth to occur.
For women, the uterine lining sheds, in the physiological term of menstruation. In rabbits, nothing happens. They just keep going in and out of heat until fertilization does occur. The same goes for cows and heifers.