"The Waters of Mars" is a special of the television show Doctor Who, one of six released between the end of Series Four and the beginning of Series Five. These specials were much like normal episodes, only longer and with bigger budgets. It starred David Tennant as The Tenth Doctor, and featured a number of actors playing one time characters.
The title and the plot are in many ways a reference to The Fires of Pompeii, where the normally confident and successful Doctor comes across a problem that he can not solve. In this case, the Doctor lands on Mars in the middle of the 21st Century, at a time and place that he recognizes as a fixed point in time. The base is set to be destroyed, from causes unknown. This event, rather than discouraging humanity, will embolden them to continue their exploration of space. If the Doctor interferes and tries to save the crew at the base, he might disrupt the entire future of the human race. In addition, it might be impossible to disrupt a fixed point in time, since how and why they work is a murky issue in Doctor Who.
We are shown what creatures attacked the base, although they remain (in Doctor Who style) gothic and unexplained. The production values on this special are higher than on another episode, so it comes across as more of a full length horror movie than a television show. Although it follows a "base under siege" plot that is well-used in Doctor Who, the scope and scale of it make it novel.
Of all the episodes of the Tenth Doctor, in the Russel T. Davies era, this one perhaps as the most character development. The Doctor, usually manic and happy, faces his own inability to save everyone. For a brief moment, he decides that he can save everyone, that he can break the laws of time, because as the last of the Time Lords, he is now the rulemaker of the universe. He is the Time Lord Victorious. In the episode's dark climax, he is disabused of this notion. It is a shock he doesn't recover from in this incarnation, and leads to the death and regeneration of the Doctor in the next special, The End of Time.
This is one of the best Tenth Doctor stories. The plot, scenery, characterization, dialogue are all well done. The symbolism of water, and how its inexorable flow is same as the flow of time, adds a layer to the Doctor Who mythology, and develops philosophical and ethical concepts that will be developed later, during the Eleventh Doctor's Series Six arc.