Can You Water Vegetables With Greywater?

Greywater is a collective name for wastewater from the shower, kitchen, washing machine, and other appliances. Using greywater to water vegetables might seem like a valid option to save money on watering costs, but is it safe for your vegetables?

You can water vegetables with greywater for a short period. If you use it, ensure to frequently rinse off your vegetables thoroughly to ensure the water doesn’t cause lasting damage and the plant is safe to eat. 

Greywater is only safe for short-term use. If used long-term, various potential problems might arise, such as reduction in soil quality, nutrient leeching, and stunted plant growth. If you’d like to find out more on why greywater isn’t always a good option and how to make it safe for use, read on! 

Why Shouldn’t You Use Greywater for Vegetables?

Greywater is mostly safe to use in a pinch, and most plants show little to no signs of danger when exposed to it over a few watering sessions. However, there are far too many variables to using greywater for longer periods without a few adjustments.

You shouldn’t use greywater for vegetables because its composition is variable. Clean water is relatively constant outside of external conditions, but since greywater comes from multiple sources, it isn’t always possible to know what it contains and account for it.

In the strictest sense, you can use greywater for many things, including watering plants. However, although you ‘can’ use it, whether you should do so is an entirely different case. 

Research shows that greywater does not usually contribute any significantly harmful effects when used for short periods. However, the problem with applying this research at an individual  level is that the composition of greywater is hard to standardize.

This challenge becomes quite real when you compare greywater and potable water.

Potable water is usually pretty clean. Also, its composition is standardized to make sure it’s good for drinking. Although the initial potable water sources (underground and surface water) aren’t always safe to drink, the water passes through filters and chemicals until it’s certified as safe.

In contrast, greywater comes from sources found all over the house. And depending on what you do in those places, the composition of your greywater can vary from being good for your plants to ruining your soil quality and plant life.

The range of probable components in greywater also brings many potential problems.

Grease Can Cause Problems for Your Plants

Kitchen water which is usually classified as greywater (sometimes blackwater), can vary in composition depending on what you’ve cooked or cleaned. If you’ve recently used a lot of oil, that grease will find its way into your drain and, eventually, your plants.

Grease is organic and will usually break down into its components given time. However, it can cause a few problems for your plants in the short term. 

The worst of these is that the impermeability of oil can make it difficult for plants’ roots to take up water. Normally, this would only be a temporal problem. But if using this type of greywater became a regular occurrence, it could be bad for plant health.

Grease typically decomposes in the soil, but with repeated greywater use, whatever decomposes gets restored, thus the level of grease in the soil stays relatively constant.

It Promotes Bacterial Growth

One major problem with greywater use is that it promotes bacterial growth. Bacteria can grow either in your greywater tank or in the water. Using this type of water on your vegetables could cause you to fall sick or alter the soil quality to the point where it could be bad for your plants.

This problem is most likely to occur if you use greywater from your kitchen as the food particles that pass into the water make it extremely conducive for bacterial growth. 

The best way to avoid bacterial growth is to use up all the water within 24 hours. Unfortunately, this leads to other problems like:

  • Waterlogging the soil.
  • Overwatering your plants.

Detergents Will Alter Soil pH

Even without factoring in problems brought from kitchen water, water from other sources can be harmful too. Your soil pH can change depending on various factors, and a major cause is the type of water you use to water your plants.

Depending on the type of detergents you use, the soil pH could be seriously affected. Most detergents are non-biodegradable, which means microorganisms can’t break them down because they contain a high percentage of inorganic compounds.

Most of these compounds raise the soil pH. Over time, this affects your plants negatively since your soil pH regulates things like nutrient uptake and the growth of beneficial bacteria. For most vegetables, the optimal pH is neutral to slightly acidic (6-7 pH). Detergents typically raise soil pH making it alkaline and unsuitable for plant growth.

It Is Expensive

A major advantage of using greywater is that it’s efficient as you’ll save money on water costs. While this is true for the short run, the cost far outweighs the savings in the long term. To use greywater long-term, you’d have to install a greywater refining system to collect the greywater from different sources. 

From there, the water either comes out through an outlet where you can collect it for use, or it passes through irrigation systems to your plants. 

Regardless of which method you go with, installing such a system is labor-intensive, capital-intensive, and time-consuming. Depending on the system’s complexity, a good greywater recycling system can cost you anywhere from $7,000 to $15,000.

In contrast, taking the highest average water bill per month ($72), you’d have to use your recycling system for more than eight years before it would have saved any money. Of course, this is only factoring in the highest possible water bill. If you live in an area where water is significantly cheaper, it becomes even less efficient.

It Could Be Illegal

Greywater isn’t always legal to use. Furthermore, because it’s still largely under-researched, there’s not a lot of uniformity in its usage. For instance, in some US States, greywater is considered sewage, similar to toilet water and its use is prohibited. 

That said, greywater can be used for irrigation in some states, while it can only be used in septic tanks in others. 

In most states, especially where greywater usage remains illegal, making the necessary alterations to your plumbing that’ll allow you to collect greywater is complex, expensive, and unrewarding. These challenges aren’t coincidental as the plumbing system is deliberately designed to make alterations difficult as well as expensive.

Furthermore, going through legal procedures to alter your plumbing is extremely difficult. On the other hand, forgoing the legal procedures could lead to heavy fines if you get caught. 

What Plants Are Greywater Good For?

Although greywater is not ideal for use on vegetables and anything edible, it has its uses. If you can reliably collect it for use, it could save you some money in the long run.

Greywater is good for ornamental plants. Since these plants are raised for aesthetics rather than consumption, the potential health risks are irrelevant. However, untreated greywater is still only good for short-term use as prolonged use can damage both the soil and plants.

You can also greywater around the house for washing clothes and flushing toilets as this won’t affect you negatively. However, your clothes’ cleanliness depends on the quality of water you use.

How To Make Greywater Safe for Use

Making greywater safe for use can be a wonderful way to increase your garden’s efficiency and save money on water bills.

Here are a few helpful suggestions on how to make greywater usable:

  • Install a greywater recycling system. Although doing so is expensive, installing a greywater recycling system will eventually save you money if you live in a place where you plan to stay long-term.
  • Don’t keep greywater for more than 24 hours. Keeping your greywater in a tank for anything longer than 24 hours can make the water highly unsafe. Besides, if your greywater contains kitchen water, there’s also an increased risk of bacterial growth.
  • Avoid using kitchen water. Kitchen water draws a lot of debate on whether it should be classified as greywater or blackwater. While it’s not always bad, kitchen water increases the likelihood of bacterial growth to such an extent that it’s better to avoid it entirely.
  • Don’t use untreated greywater long-term. Long-term use of greywater will eventually lead to problems with your soil pH and the quality of your plants.
  • Never use it for vegetables and fruits. If you’re raising plants for food such as vegetables or fruits, it’s extremely important to keep greywater away from them as it can render them highly unsafe to eat.

The Verdict

Your best bet is to stay away from greywater. Although you can use it in a pinch, the number of problems that can result from using it far outweigh the potential benefits. Therefore, use greywater for the short-term if you have no choice because long-term use can cause health and legal problems.

You can read my other article on watering plants with soapy water here: Can You Water Your Plants With Soapy Water?

Alexander Picot

Alexander Picot is the principal creator of, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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