Huge numbers of explorers died because there was no alternative, today we have alternatives. A launch failure that killed people could happen and it would be a disaster, but it's far less likely than a mission failure that kills the crew. The main thing is that unmanned missions are far cheaper and far simpler. You don't need human rated rockets, you don't need life support, you don't need to carry food, you don't need to dispose of bodily waste, you don't need to solve the huge problems of crew comfort and preventing muscle atrophy in zero G. There is a large array of problems and challenges you can simply bypass and not worry about. The end result is much like any other form of automation, automate the factory and you get people out of dangerous jobs, you greatly increase productivity and consistency while greatly reducing cost. At least in automating space missions you aren't putting millions of working class people out of a job. I don't have the numbers offhand but we can probably send out *at least* a dozen or more robotic explorer missions for the cost of one single manned mission and we can send them to places far too distant to send humans in a reasonable time scale. That's another big problem, Mars is the nearest planet, it takes months to get there and we've already sent rovers there. Where is the next closest planet that has conditions within the realm of human survival and how many centuries will it take to get there?
There are many deaths of brothers and sisters of my own ancestors who also tried to colonize North America pre 1700. All told around 30% of those that tried died on the voyage, or within a year of reaching North America. Yet members of my ancestral families kept sending their own over knowing full well others in their own families who had gone before had died. Many of my relatives are also the survivors of those that initially settled the midwest. Quakers would initially set up a town, and move their families there. Then others would move in. Eventually the area would get filled in by farms, non Quakers, etc. A bunch of young men with new families would go and setup a new town further west, and send for their wives and children once the houses were up, and crops were soon to be harvested. Many would die from raids on the new frontier towns, yet they kept at it, generation after generation.
Deaths trying to explore and colonize the moon or Mars are inevitable. The people who are willing to try, know they may die. That is life being an explorer or pioneer.
As for water, their is plenty on Mars. New outflows are being seen all the time. Looks like some drilling and maybe heating is what is needed to get at it. Habitats, what do you think the tunnel boring company Musk owns is for? You can sleep quite a few people in nice accommodations in a kilometer length of tunnel 30 feet in diameter. Some researcher had written an AI based control system for earth movers so a bunch of them could make the initial hole for placing the boring machine in before humans arrived. A large landing site could also be graded flat right next to the pit for the excavator and boring machine flights to land at. The site can be fully prepared and all the tunnel boring machinery landed before the first humans arrive. If you send 6 boring machines distributed over 28 rocket loads, loss of a half won't stop the program. In the process you learn how to land large loads long before any human makes the trip. My expectation is they will use a minor modification of the booster landing systems to land most of the initial supply loads on Mars. To save fuel, a huge airbag system could be used for initial atmospheric slowing to get down near to orbital speeds, then jettisoned before final decent on the booster rockets. They have been experimenting with bringing large booster sized craft in sideways so the heat of reentry is spread over the whole carbon fiber side rather than just the small end. That may be all they need for braking at Mars. Landing on mars will be routine by the time humans go. I also bet they will eventually refuel them and fly them home for reuse. Water can be cracked into hydrogen and oxygen which are great rocket fuels. Just design an engine that can have it's core replaced with a H2 O2 fuel system. The rock and mineral samples sent home in one of them would be a gold mine for researchers back on earth. It would be nothing to send back a few thousand kg of samples gathered from all over on each return flight. Those samples then could be analysed back on earth and construction materials developed from them. Except now there will be thousands of kg to work with. Construction materials for the moon have already been proposed and some even developed based on the small samples returned.
PS, I bet once large loads are successfully landed on Mars, world wide public interest will explode. Sometime go and read about the world wide interest in the US space program during the Apollo missions. I think Musk's biggest hurdle will be not having his effort nationalized.