It's easier than hauling all the water they need up into space
And just imagine how difficult it will be with a distant lunar or planetary colony.
YOU don't have to drink water this way. The astronauts who make a great deal of
personal effort to get into space know and accept all such risks and issues. Drinking
filtered water from urine is not their top concern.
And I would usggest if you are squeamish that you should not see what is taken out
of most drinking water before it gets to you -and what does escape the filtering.