إذا كان مع المسافر إناءان طاهر ونجس لا يتحرى بينهما بل يتيمم
If a traveler has two vessels, one with pure water and one with impure water, the cited Hanafi ruling does not choose by estimation in this particular circumstance; tayammum is performed.
The stated reason is that water has a legally recognized substitute for purification. With no reliable identification of the usable vessel, the presence of that substitute changes the ruling.
This is a specific classical case involving uncertain water. Other details of identification, quantity or necessity require their own legal assessment.