So let's take meat (and all animal products) out of the picture altogether. It takes far too much water to produce animal-derived foodstuffs, and from an environmental perspective, it just doesn't make sense. But let's say you don't give a toss about the environment, and let's say you don't believe we should be wasting time and energy on animal rights when there are so many more pressing and important human issues. Fine, then let's start with water.
Water. We need it, we're made of it, and no single living entity can survive without it.
It's a basic thing, right? So why isn't it also a basic right? Again, let's forget for a moment about those pesky animals that vegans are always going on about. What about the right for all humans to have access to clean safe water? And if so many around the world are going without, is it ethical to be pumping all that water into food items that aren't healthy and aren't necessary? And what about water privatization? Not surprisingly, there are corporations who want to make money off of a substance that should be a basic human right. Perhaps the air we breathe is next?
So even if the only thing you care about in relation to water is that all people on this planet have enough to drink (we're not even talking about the starvation issue here), then one of the first steps you need to take is to go vegan. It's time we rethink the ethics of water, reconsider our current consumption mode, and acknowledge that water isn't a market resource, but part of a natural living ecosystem that all beings depend upon.