Leading pump manufacturers, such as Davey, recommend the use of First Flush Water Diverters to help extend the life of pumps.
Typically pumps utilise a mechanical seal to ensure water does not penetrate into the pump's electric motor. First Flush Devices help prevent sediments and other debris from:
1. Wearing down the seal (which can result in pumps leaking),
2. Getting caught in the pump impeller,
3. Jamming up other pump components.
The Installation and Operating Instructions (as at 29 March 2006) of the Davey Rainbank, an innovative product that allows the priority sourcing of rainwater, only using mains water as backup, make the following recommendation:
"Your rainwater tank may be required to be installed with a first flush diverter. Installing a first flush device is essential to reduce the introduction to the rainwater tank of sediment and other materials which can polute the water. Even where it is not a requirement of your local water authority, Davey recommend the use of a suitable first flush diverter and/or rainwater inlet strainers."
Link to instructions.