By Jill Richardson Guest Columnist I just got back from hiking 95 miles in the Sierras. (Yes, just like that Reese Witherspoon movie Wild, only far fewer miles.) I returned from my trip with something eating at me. Backpackers are supposed to \u201cLeave No Trace.\u201d It\u2019s not just a nice concept, but a specific set of rules we follow \u2014 even when we go to the bathroom. You dig a hole at least six inches deep before doing your business, and you bury it. And you do that far enough away from lakes and streams to prevent contamination of the water we all drink. You\u2019re even supposed to take your used toilet paper with you when you leave, because nobody wants to feel like they\u2019re hiking in a bathroom. Obviously, you clean up and pack out your trash, too. Serious hikers are fastidious about doing those things. Some go so far as to hide evidence of their campsites before leaving by scattering twigs and stones over the spot where their tent was. And it\u2019s not uncommon at all for hikers and backpackers to police one another. Don\u2019t ever tell anyone else you didn\u2019t pack out your used toilet paper unless you want to catch hell for it. But Leave No Trace seems to extend only to the easily visible: trash, toilet paper, bodily functions, and so forth. Anything you can\u2019t see with the naked eye \u2014 like sweat, detergent, sunblock, mosquito repellent, pesticides, and other chemicals \u2014 seems to get a pass. Again and again, I saw hikers bathing and doing their laundry and even washing dishes in lakes and streams. And this is the water that we all drink. Sure, we filter it, boil it, or chemically treat it before drinking it. But those methods are designed to kill off microbes, not to remove the chemicals in consumer products. What\u2019s more, all of the plants and animals rely on that water too. The insects, which provide food for birds, reptiles, and other animals, need that water. The trout, that hikers like to catch and eat, live in it. I want to eat trout with butter and lemon as seasoning, not with pesticides and detergent. Many conscientious backpackers at least go to the trouble of packing biodegradable soap. But your clothes carry residue of your laundry detergent from home, as well as your sweat. Some treat their clothing with pesticides to help with the mosquitoes. Others treat gear with waterproofing chemicals. Then, of course, everyone slathers bug spray and sunblock all over themselves. The bugs were bad this time, and the sun is intense at high altitudes. I understand using those chemicals. But don\u2019t rinse them off in the stream. The alternative to bathing and washing in the stream is only slightly more work. You gather some water, haul it a few hundred feet, and use it to do your washing where it won\u2019t contaminate an entire river. The reason why I share this, presumably with many who will never backpack in their lives, is because it seems to reveal a more general truth about humanity: We underestimate or ignore what we cannot easily see. Between the chemicals rinsed off in the streams and the toilet paper so carefully packed out, the chemicals harm the environment more. But it\u2019s the toilet paper, which we can see, that gets the attention. Back in the \u201creal world,\u201d with trash service and running water and flush toilets, our interactions with the environment are easier to ignore. Here, we never have to worry that going to the bathroom in the wrong place could result in contaminated drinking water. But whether in the wilderness or in the city, it\u2019s dangerous and harmful to discount the impact of what we can\u2019t see, just because we can\u2019t see it. OtherWords columnist Jill Richardson is the author of Recipe for America: Why Our Food System Is Broken and What We Can Do to Fix It.