With growing concerns about runoff and contaminated water, homeowners with private wells are concerned about using chemicals in the yard and how it could affect their water supply.

We all know that we should be extra careful when using pesticides on our property, but does lawn fertilizer pose a risk to well water? Is it possible to keep lush, green turf even if you have a well?

While not immediately as dangerous as pesticides, lawn fertilizers are high in nitrates, which can be dangerous if leached into your well water. Before applying lawn fertilizer, consider your well’s location, depth, and get your water tested regularly. Also consider using slow-release or organic fertilizers that will release nitrates more slowly into the soil.

Effects of Chemical Fertilizers on Groundwater

The key component of lawn fertilizers that you should be concerned about is nitrate.

Nitrates are a readily absorbed form of nitrogen that plants can use to promote leafy green growth. Since grass is primarily grown for its leaves, lawn fertilizers always have high levels of nitrogen.

The problem for those with wells is that nitrates are also highly soluble in water and can easily leach down soil layers to the groundwater.

Nitrates are commonly found in small amounts in well water, however high levels of nitrates are dangerous, especially for babies and young children. Nitrates interfere with oxygen transport in your blood.

If you are using your well water for drinking, cooking, or giving water to livestock, always test it regularly (at least once a year) for nitrates.

Applying Lawn Fertilizer Safely If You Have a Well

1. Consider your well’s location and depth

Where and how deep your well is will dictate how likely it is for fertilizer to seep down into your well water.

Consider the overall grade of your property. A well that is located higher up on a slope will be less affected by lawn fertilizer use, as the fertilizer will leach downward and away from your well.

At the same time, if your lawn is near a downhill stream, heavy rain could wash chemical fertilizers into the stream which will recharge groundwater with contaminated water.

Another key factor is the depth of your well. Shallow wells are more susceptible to being affected by nitrate leaching than deep wells.

One more factor is the type of soil you have. High clay soils are more compact and will likely not leach fertilizers down into groundwater directly, but are more susceptible to runoff, which could indirectly affect your well water. At the same time, very sandy soils will allow nitrates to percolate straight down into your groundwater.

Example: If your lawn is uphill from your shallow well, I would advise against using liquid lawn fertilizers entirely. You might want to consider a light application of slow-release fertilizer or organic granular fertilizer, and test your water for nitrates at least once a year to check for possible nitrate buildup.

2. Use organic lawn fertilizers

Organic fertilizers work differently from conventional chemical fertilizers in that they require soil life to break them down and release their nutrients. This means that fewer nitrates will be released into the soil all at once, and will most likely be taken up by grass before it can seep into your groundwater.

For organic options, you can use either a liquid feed or granular fertilizer. Granular fertilizers are generally recommended as they offer a slower, continuous release and therefore require fewer applications.

Good examples of organic lawn fertilizers are Dr. Earth Lawn Food (3-0-1) and Down to Earth Bio-Turf (8-3-5). These have a good amount of nitrogen (the first number), which is critical for green turf growth, but also provide phosphorus, potassium, and micronutrients for healthy, vibrant lawns. However, any organic, balanced NPK fertilizer will work on lawns.

3. Test your well water regularly

The Groundwater Foundation recommends testing private well water at least once per year, and more often if you have a shallow well.

In addition to well water tests for bacteria, sulfates, pH, and heavy metals, you should get a nitrate test, as this will show the impact of fertilizer use on your lawn. Nitrate tests are a standard test, but make sure it’s included in your water tests.

You can also get a separate nitrate test. These typically run for less than $50, depending on your location.

Note that nitrates can also come from other sources, such as a nearby septic tank.

My Well Water Has Nitrates – What Can I Do?

If your water test comes back positive for high levels of nitrates, immediately stop using your water for drinking or cooking. It can still be used for irrigation or other purposes.

Fortunately, there are ways to remove nitrates from drinking water. The CDC suggests distillation, reverse osmosis, and ion exchange as effective treatments to remove nitrates. Boiling water or using mechanical filters like charcoal won’t remove nitrates. Get in touch with your local health department for more advice for your area.