It can be staggering to think that nearly half of all above-ground water sources are contaminated by things we do at home. What we put down the drain inside our homes and let go down the storm drain outside all take their toll.

You need to know what the biggest polluters are. Here’s a list of five things that should never go down the drain.

Grease

It sure is tempting to pour used cooking grease down your sink drain. But that grease not only backs up your drains but those in your neighborhood, too. That’s because when grease hardens, it can easily clog up sewage pipes and can actually force raw sewage back into your home or into the homes of others on your street.

I keep a large container under my sink to collect cooking grease, and when it’s full, I take it to a full-service recycling center. Sure, it’s a little more work but a whole lot more pleasant than dealing with the alternative.

Used motor oil

Whatever you do, don’t pour oil down a storm drain. Those drain directly to local waterways and just a gallon of motor oil can contaminate 1 million gallons of water. Used motor oil is another item you’ll need to drop off at a full-service recycling center. And, if you go somewhere to get your oil changed, make sure to support those businesses that recycle their used oil.

Fertilizers, pesticides

Excess nutrients are another major source of contamination. When we use too much fertilizer on our yard, the excess is picked up by stormwater runoff and dumped into our waterways. This nutrient overload causes algae to bloom, which removes oxygen from the water. That literally chokes the life from vital water creatures that help improve the water’s quality. To avoid all that, use only the amount of lawn chemicals you truly need and only when and where you need it.

Old medicine

If you have medication you are no longer taking or is past its expiration date, don’t flush it unless it specifically says so on the bottle. Instead, throw the medicine in the trash in a sealed bag with coffee grounds or find a responsible medicine disposal company. Many pharmacies partner with companies that will take care of your old prescriptions properly, and some of those companies allow you to return your medications to them directly. Go to DoYourPart.com/Columns for more resources.

Pet waste

And finally, don’t forget to scoop the poop. Pet waste is considered raw sewage because it contains parasites and harmful microorganisms that can be transmitted to humans. When it rains, these parasites and bacteria can be washed into nearby storm drains. Best to clean up after your pet and dispose of it in the trashcan.