I'd do the following...

1. Get WaterUseConnections objects
2. Use the HVACComponent function loop to get their respective plant loops
3. Use the Loop function supplyComponents to get all supply components for the loop returned as a model object vector
4. remove the existing objects
5. Create your new object
6. Use the PlantLoop function addSupplyBranchForComponent to add the new object to the loop

Hopefully that helps.