10 tips to safely irrigate your garden using a greywater system

Greywater is a great resource for watering your lawn and garden. A greywater system can distribute the water through sub-surface irrigation or surface irrigation. Here are 9 top tips to make sure that greywater is applied safely water your garden that is good for the environment and your health.

1. Use large water droplet size sprinklers

Use spray heads that produce large water droplets (not ones that produce mist) to prevent spray drift and ensure that the water is primarily distributed within the designated irrigation field. Greywater surface irrigation (above ground) is only applicable for a Greywater Treatment System (GTS) where greywater is treated to a higher quality.

2. Check for signs of plant damage

A good indication of irrigation rate is to monitor plant health and soil structure. Thriving plants, green lawns and soil that isn’t drying out is a healthy sign that the greywater system is providing sufficient water for plant growth and there is even distribution throughout the irrigation area.

3. Don't reuse greywater during Winter

Allowing greywater to be used in the irrigation area during Winter or heavy rainfall runs the risk of your plants being overwatered. To do this is easy, just turn the handle located in the diverter box to divert greywater back to sewer in Winter and heavy rainfall periods to ensure the soil aren’t oversaturated.

4. Place warning signage in the irrigation area

Use warning signs at all greywater outlets and at the boundaries of the irrigation area to include “Recycled Water – Avoid Contact – DO NOT DRINK”

5. Use correctly marked irrigation lines for greywater use

All irrigation must be coloured purple (per Australian Standard 2700) and are clearly marked with the words “Recycled Water – Avoid Contact – DO NOT DRINK”. You can view examples of the marking, labelling and signage of greywater installations.

6. Measure out all setback distances and make sure these can be achieved

Ensure all setback distances are met. There are different horizontal setback distances that apply for subsurface and surface irrigation areas. Softened ground from irrigation can affect the structural integrity of certain structures including buildings, fences, retaining walls, embankments etc. Oversaturation can also cause overflow across boundaries and onto pathways. Keeping within the confines of setback distances allows for a safe distance in the case of greywater overflow in the system.

7. Use phosphate-free washing detergents

Use environmentally friendly detergents that are biodegradable and low in phosphorus, sodium, boron and chloride. Read more about phosphate-free washing detergents. Household products including washing detergents can be high in nutrients and salts. Excess phosphorus content can be toxic to some plants, especially native plants. The best solution is to look at the phosphorus, salts and nitrogen percentage content of washing detergents that is displayed on the label. You can find a list of washing detergents and the label contents in Australia at www.lanfaxlabs.com.au

8. Use washing detergents low in salt

Salts are commonly used in washing detergents as fillers. Use washing detergents low in salt for example using a powder concentrate or a liquid washing detergent. Excess salt that ends up in greywater can increase soil salinity and affect soil structure. Salt can quickly accumulate and crystallise around plant roots, making it difficult for the plant to draw water from the surrounding soil. Overall, salt within the soil can also prevent water from being absorbed by the soil.

9. Apply a soil wetting agent every six months

In addition to excess nutrients, salts and chemicals in common household products, greywater can contain fats from soaps and fabric softeners. This can cause the soil in the irrigation field to become water repellent and absorb less water. A soil wetting agent is a substance that allows liquid water and fats to easily mix together and help more water to penetrate into the soil. A 2kg bag of granular soil wetter starts from $9.58 and can treat up to 66 square metres in area.

10. Check the soil pH for the first six months

The pH of soil and soil structure is integral to plant health which can be affected by various contaminants in greywater. A significant change in the pH can also cause iron deficiency in plants where new leaves may appear yellow with green veins. Different plants prefer high or low pH but most plants will grow well in a more neutral pH (6-7).

Check the soil pH weekly for the first six months to see greywater performance on the soil. With many household products causing greywater pH to alter, it can be difficult to pinpoint which product is causing that significant change. You can add organic matter, like compost, to the soil which acts as a pH buffer to help neutralise the pH and improve soil health. Another consideration is to replant vegetation that prefers the new soil pH if it has changed after six months of greywater irrigation in that area.

A home pH soil test kit can start from $18.30 or you can use an electronic pH meter starting from $14.99