Prime is excellent, ageing water is also OK, but my favourite method is to use a HMA filter. I attach the HMA unit, which looks similar to an RO unit, to my kitchen mixer tap or shower output via a hose. The output from the HMA goes via hose to fill the tank. No more carrying buckets, no more huge containers of water hanging around the house. The HMA dechlorinates, removes chloramine, heavy metals and other nasty things from tap water. This is the unit I have. https://collinswaterproducts.co.uk/product_info.php?products_id=183&osCsid=3f8a3d1d2040a3f665f51e512922f04f
This is the impressive list of what it removes:
A 5 -Micron Sediment Filter Made of 100% Pure Polypropylene Fibres. Removes Dirt, Sand and Rust.
A Granular Activated Carbon Filter Composed of High - Performance Activated Carbon. Removes Free Chlorine, Odour, Organic Contaminants, Pesticides and Chemicals.
A HMA ( coconut , carbon, kdf mix) filter. Removes Chlorine,Chloramine, amonia heavy metals, Trihalomethanes, Pesticides, Volatile Organic Chemicals and 99.95% of Giardia and Cryptosporidium Cysts.