i have one of those three quart models too and had bought the blue, chemical cleaning powder the manufacturer recommended which i use a few days till i read the vinegar solution here on the forum months back.
here in nc, we have municipal wells. the water quality isn't dreadful but still it's 'imperfect' enough so i use a vinegar soak for a few hours to dissolve the residue after each batch. beautifully, just the bottom 'well' of the stainless tub needs to be filled AND you can re-use the quarter cup or so of white vinegar again and again — till it looks too grungy :).
i do have a brita in the fridge i never use now and mh's point — the purer the water you start with the easier it is on the distiller — never occurred to me, figuring the 'work' of the distiller is just to boil the water and the debris doesn't make that harder (— does it? —) as it just doesn't get boiled away or passed over into the collection jug.
i would like this distiller to last forever, so i may try using brita water and see if there's less debris — or if the final product tastes better.