A 61 kL tank is a storage volume. An 80 kL/day plant is a treatment rate. Neither figure alone establishes how long a site can operate through an interruption: consumption, supply priorities, available water and controls are also part of the assessment.
Backup-water planning starts with the uses that must continue, the demand those uses create and the exposure to supply interruptions. Storage turnover, pumping and changeover connect the tank to a useful site supply.
Brief the project.
Use the information you have to start a conversation. The source, demand and final-use requirements can then be refined for the site.
Discuss your project