What is greywater?

Greywater is the wastewater generated from everyday activities such as laundry, bathing, and kitchen use, excluding toilet wastewater (known as blackwater). Greywater is an abundant resource since we produce it daily. The good news is that with minimal effort and cost, you can divert greywater to nourish your garden. This can be as simple as setting up a DIY system using a greywater diversion hose connected to your washing machine or opting for a full-scale commercial greywater system.

Considerations when using greywater

Regardless of your choice, there are essential factors to consider:

• Greywater reuse is not a one-size-fits-all solution. Your circumstances and location will influence the type of system that suits you best. Therefore, it's vital to conduct thorough research to ensure your greywater system aligns perfectly with your specific needs.
• The quality of greywater varies depending on what goes into it. Generally, greywater has low levels of pathogens and bacteria unless you're washing contaminated items like diapers. Selecting the right cleaning products is crucial for safe greywater reuse. Elements like phosphorus and nitrogen in greywater can serve as nutrients for your plants, reducing the need for fertilizers. However, excessive salt and high pH levels can harm your soil and plants. To mitigate these issues, choose cleaning products with low salt content and monitor your soil's condition.
• One of the primary concerns with untreated greywater is salt buildup in the soil, primarily from powdered washing detergents and fabric softeners. Sodium salts, commonly used as bulking agents in these products, are the main culprits. While concentrated powders and liquid detergents contain fewer salts, many powdered detergents now offer low or sodium-free options.
• Untreated greywater tends to be alkaline, which can affect your soil's solubility and, subsequently, your plants' ability to absorb nutrients. pH values range from acidic to alkaline, and the pH of your greywater source can vary. If you have acid-loving plants, your choice of cleaning products becomes critical. Washing powders and solid soaps tend to increase pH levels, while liquid soaps are generally more pH-neutral. Regular monitoring and soil conditioning can help you maintain the ideal pH level for your garden.
• Apart from salt and pH, greywater contains fats, oils, disinfectants, bleaches, toothpaste residues, and even hot water. These elements can impact your soil and plants, so it's essential to understand their effects and take precautions.

Types of Greywater Systems

Greywater systems can be categorized into three main types: diversion-only, diversion and filtration, and diversion and treatment. Each has its advantages and regulations, making your choice dependent on your specific circumstances and location.

1. Diversion-Only Systems

Diversion-only systems are the simplest and most cost-effective. They can range from manually bucketing greywater to using three-way valves on shower or laundry wastepipes. However, be cautious when using the hose-on-washing-machine method, as it can strain your washing machine pump. To avoid potential issues, consider a surge tank near the laundry to accumulate water gradually.

2. Diversion and Filtration Systems

These systems filter out particles like hair and lint from greywater before distribution. Filtering is mainly to prevent clogs in your irrigation system. Some commercial systems come with lint filters that can be cleaned periodically. They often use surge tanks to regulate water flow and prevent pooling or overwatering.

3. Diversion and Treatment Systems

Treatment systems offer various methods, including biological and chemical processes or a combination of both, to treat greywater. Treated greywater can be used for various applications, such as laundry washing. However, treatment systems tend to be more expensive and require ongoing maintenance and water quality testing.

Irrigating with Greywater

Distributing greywater efficiently in your garden can be a bit challenging but is equally important. Several irrigation methods are available, including agi-pipe, drip irrigation, and mulch basins, each with its pros and cons.

Calculating Water Needs

To determine how much greywater your garden needs, you can calculate your soil's irrigation rate, the area to be irrigated, and seasonal variations. Matching your greywater output to your garden's water requirements is essential.

Dos and Don'ts of Greywater Use

Using greywater comes with some common-sense rules to minimise risks:

• Wash your hands after watering with greywater.
• Divert greywater to the sewer during wet periods.
• Use biodegradable and low-sodium, low-phosphorus cleaning products.
• Avoid using greywater containing disinfectants and bleaches.
• Don't store untreated greywater for more than 24 hours.
• Refrain from using greywater on raw-eating vegetables or herbs.
• Avoid using greywater from washing nappies or heavily soiled clothes.
• Exercise caution with kitchen greywater, unless it's treated.
• Prevent greywater from leaving your property.
• Don't use hot greywater, as it can harm beneficial organisms in the soil.

Want to find out more?

See a greywater system buyer's guide.