Verb Tenses & Mood

some one please reply to this question

chaitanya.mehrotra wrote:Original:Water freezes if it were cooled to zero degrees Celsius

Correction: Water freezes if it is cooled to zero degrees Celsius

Doubt:I can make out by reading that is should be used but the official explanation below about subjunctive mood / indicative mood is not clear.

Were (present tense of the hypothetical subjunctive mood) should be is (present tense of the indicative mood). This sentence is stating a general rule that admits of no uncertainty, so the if-clause must be in the indicative mood. You can also omit a tensed verb altogether from the if-clause: Water freezes if cooled to zero degrees Celsius

"Were" with a singular subject in an "if" statement is used when the author is talking about any hypothetical situation.
Ex: If I were a rich man, I would travel around the world.
This sentence means that presently I am not rich. I am talking about a hypothetical situation.
But the sentence: Water freezes if it were cooled to zero degrees Celsius, is talking about a general rule and not any hypothetical situation and hence it should be - Water freezes if it is cooled to zero degrees Celsius.

Hope it helps!

moreover its a rule to use sentences in present tense which are universal facts and rules or quotes

What is the meaning of present tense of hypothetical subjunctive mood and present tense of indicative mood?
Can someone explain with examples ?
Hypothetical subjunctive is only - Simple past forms or were.