Commercial rainwater tank cleaning case study in Brisbane
The following details of a commercial rainwater tank cleaning case study in Brisbane highlight the problems when poor installation during the construction and installation of a large commercial rainwater harvesting system result in unnecessary expense and inconvenience to the tank owner and the section of a community directly in contact with the stored rainwater.
The commercial rainwater tank system consists of numerous in-ground custom-built concrete tanks of a total capacity of approximately 480,000 litres at a large residential unit complex. The rainwater is being used for toilet flushing and laundry in the individual units and for irrigation of the common garden areas.
Property administration contacted Water Tactics to inspect the rainwater system after complaints regarding the stored water quality. Residents had experienced smelly tank water and discoloured water in the toilet and laundry.
Identifying the problems
After conducting a thorough inspection of the rainwater system, we concluded that the water problems were due to the following:
- Absence of pre-storage water filtration. A gross pollutant pit is generally the minimum level of filtration required for underground tanks of this capacity and generally followed by a finer level of pre-storage water filtration. There had been no attempt to pre-filter the rainwater. Pre-storage filtration is fundamental in the prevention of debris from entering the tank. Additionally, if serves to preclude the entry of vermin and mosquitoes. The MPMSAA Rainwater Tank Design and Installation Handbook describes this requirement in detail.
- Contamination of rainwater by cross-connection with grey water. A grey water system had been installed with waste directed to the stormwater system. We can only conclude this must have been an oversight in the original grey water system installation and overlooked during the plumbing inspection.
- Significant building debris had entered the tanks during the construction phase and had not been removed prior to the rainwater harvesting system being made operational.
A successful outcome
We were able to provide commercial tank cleaning services to successfully de-sluge, clean and disinfect all tanks. Using confined space entry procedures and safety measures, the work was undertaken over two days. The base causes of the rainwater contamination were identified and reported to the tank owner along with recommendations for rectification of all issues.
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