What does aluminium in water mean in practice?
Solubility changes strongly with pH, so a total result does not always describe the fraction passing through a filter.
When does it matter?
Elevated aluminium may cause turbidity or deposits and indicate poor coagulation or material corrosion.
Which solutions are related to it?
Identify the source and form first; treatment may use pH control, coagulation and filtration, adsorption or RO.