I don't have a Seiko Astron in my collection. However, I do have a lot of Seiko. The list of warnings you gave is not uncommon. If you allow me to explain, I believe this is what the manufacturer is concerned about:
"1)do not pour running water direct on faucet" - do not subject the watch to the pressure of a jet of water. A jet of water with enough velocity can easily exceed the water resistance of the watch.
"2)Do not leave moisture, sweat and dirt on the watch for a long time" - chemicals in those material over time can degrade the materiel of the watch. In the same way that we need to dry our cars after a wash to eliminate water spots.
"3)Do not wear the watch while taking a bath or a sauna .(Steam, soap or some components of a hot spring
may accelerate the deterioration of water resistant)" - similar to number (1) and (2). In the case of hot spring, the sulfer in the water is a real silent destroyer as it is acidic in nature.
Under normal circumstances, your Astron shouldn't face any problems.
