Water and Lava: You can collect source blocks, but they will reappear shortly after being collected. Dropping them will create a source block temporarily, but it will not spread. Instead, it will disappear after some time. Other players never see the source blocks you place. As a workaround, a server admin can give a player (by using the /give command) source blocks (id 8 for Water, id 10 for Lava) to place in the same way any other block would be placed.