Over 2 million people stay overnight when visiting the Mornington Peninsula each year, making it one of the largest short stay rental accommodation destinations in Australia. Homes that rely on Onsite Wastewater Management Systems (OWMS) to treat wastewater on their property can experience significant strain during periods of temporary high occupancy, as these systems are not designed for high or fluctuating use.
OWMS are designed and approved based on the number of bedrooms, assuming number of bedrooms plus one. For example, a 4-bedroom home is calculated as being occupied by 5 people. The design flow rate per person is 180 litres per day which equates to 900 litres in total per day. They are not sized for the maximum number of guests that might stay during busy periods. When short-stay rentals regularly host more people than the system was designed for, especially in short bursts (weekends and holidays), the system can easily be overloaded. This can:
- Push wastewater through the system too quickly, so it is not properly treated.
- Cause sewage overflows, odours and system failure.
- Increase the risk of harming local creeks, groundwater and coastal waters.
- Increase risk to health of guests and wider community.
- Lead to expensive repairs or full system replacement for owners.
For short-stay properties, good management and guest education are essential to prevent these issues. A specific Guest Guide – Wastewater (septic) Care fact sheet can be downloaded here(PDF, 176KB) . It can be printed and included in the short stay rental or added to guest instructions.
What short-stay hosts and managers should do:
If you own or manage a short-stay property with an OWMS, follow these essential practices to protect your system, the environment, and community health.
Know your system’s limits
- Check your permit and system design details. As mentioned, OWMS are typically sized based on the number of bedrooms, assuming one person per bedroom plus one. If your property regularly hosts more people than this, even for short periods, the system may become overloaded and fail.
Service and pump out more frequently
- Under the Mornington Peninsula Shire’s Community Amenity Local Law 2022, property owners must ensure their onsite wastewater management system (OWMS) is inspected every three years and desludged as required by a qualified contractor. This is designed to protect public health, the environment, and community health.
- For short-stay rental properties, which often experience high and fluctuating usage, more frequent desludging, such as every two years may be necessary to prevent failure. Do not wait for issues like odours or overflows to appear. Proactive maintenance helps reduce the chance of issues during inconvenient or busy periods, protects your property, and the community.
Land Application Area (LAA) maintenance
- Maintain your LAA. Keep grass or shallow-rooted vegetation trimmed to support growth and effective evapotranspiration.
- Do not plant large trees or woody vegetation near the LAA as roots can damage trenches and sub-surface drip irrigation.
- Don’t drive or park vehicles over any part of the system, including the tank or LAA. Heavy loads can crush pipes and compact the soil leading to system failure and costly repairs.
Reduce wastewater volume and surges
- Install water-efficient fixtures and appliances.
- Encourage guests to take shorter showers of around 4 minutes, and to use the washing machine and dishwasher only when full, preferably on eco mode (this aligns with Victorian Government water-wise advice Top tips to help you be water wise at home).
- Encourage guests to stagger use of appliances and water consumption (for example, not running long showers, the washing machine and dishwasher all at once) to avoid sudden high flows that can overwhelm the system. Utilising timers on machines can be a very useful technique for staggering use.
Limit solids, lint and food waste entering the system
- Fit lint filters on washing machine outlets to reduce fibre load, and clean or replace them regularly.
- Do not use garbage disposal units (in-sink food grinders). These greatly increase solids and organic load on the system. Use sink strainers and scrape food scraps into the bin instead.
Maintain filters and keep maintenance records
- If your system has an effluent outlet filter, ensure it is cleaned at every service and or as required by your service provider. This prevents solids from reaching and clogging trenches or irrigation lines.
- If your system does not have one, consider installing a filter to improve performance and reduce maintenance issues.
- Stay on top of all required quarterly servicing for secondary treatment systems, and keep detailed service records, including maintenance logs and pump-out dates. Good record keeping supports system longevity and demonstrates responsible management of a rental property.
Use septic-safe products
- Choose biodegradable or septic-safe shampoos, conditioners, soaps, detergents and cleaning products that are low in phosphates and salts.
- Avoid routine use of bleach or strong disinfectants, which can damage the beneficial bacteria in the tank that are needed to treat wastewater.
Provide clear information to guests
- Include short-stay rental septic tips in your booking information and house rules.
- Install simple, clear signage in kitchens, bathrooms and toilets to remind guests what can and cannot go down the drains, and how they can help reduce water use.
- A Guest Guide – Download the Septic Care fact sheet(PDF, 176KB).
Plan ahead for System Issues
- Keep contact details for a licensed wastewater contractor who can respond to issues like overflows or blockages.
- Contractor availability can be limited during peak holiday periods, making preventative maintenance essential to avoid disruptions.
- Provide guests with simple instructions for reporting problems such as odours, slow drainage or wet areas. A fast response helps protect your reputation and avoid negative reviews.
- Council has a list of local pump out contractors and service agents which can be provided to owners on request.
- Council also has a free onsite system assessment service that includes assisting in identifying the type of system and appropriate maintenance needs, as well as locating the system. To book an appointment contact the Environmental Health Team: (03) 5950 1373
- You can check if a sewer connection is available to your property by contacting South East Water Pressure Sewer Connections: 1300 733 098.
By managing your system carefully and helping guests understand how to use it, you are meeting your General Environmental Duty (GED) under the Environment Protection Act 2017 and helping to protect the Mornington Peninsula’s unique environment for the whole community.