Sentence Correction (SC) | Re: Sophisticated laser-guided land graders can now flatten uneven

Hello Dear experts,

there is a split between,

waste rainwater in runoff down sloping fields
and
rainwater is not wasted in runoff down sloping fields.

I think it slightly changes the meaning as one is modifying rainwater and other is modifying wasted.

Or its completly based on so that vs so as not to.

IS there a general "one" straight rule to distinguish between so that vs so asto?