The antonyms for the phrase "are wasteful with" are being careful with, conserving, thrift, economical, stingy, frugal, and efficient. These terms indicate that the opposite of being wasteful involves being mindful of how one uses resources, whether it be money, water, electricity, or time. When someone is careful with resources, they use them efficiently without unnecessary waste, thereby saving money and reducing their environmental footprint. By switching to these antonyms, one can adopt a more sustainable lifestyle that not only benefits them but also the planet, allowing us to create a better and more efficient world for the present and future generations.