I've got a 'first clean' to do on a place tomorrow - Well, it's kind of a first clean, it's a music shop that belongs to a friend of the family so I said i'd hit it with the packpack to clean all the frames and sills and paintwork etc. It's a favour really (only charging a tenner) as he's a good mate but there are a lot of glass and frames - here's a pic So what I was thinking of doing, is half filling the backpack from the tap, then pouring in a kettle or 2 of hot water then topping it up so I have 'warm water' - using this to do a first clean to clean all the frames and etc etc, then having a coffee and a cigarette with him while it drips and dries and then refilling with pure water and doing the glass again. I know that whatever is left of the tap water will raise the TDS but if I empty it out, slosh a bit of pure water in there, then empty that out, then refill with pure water, it should be fine right? As i've said hes a mate and I usually do this one trad, weekly, so I don't think he will care if it spots a bit, but I don't want to damage my backpack using hot water / tap water? Am thinking as long as it's just warm / lukewarm rather than 'hot' it'll be fine? Will prolly squirt some ecover on the brush too. Thoughts? Genius, or idiocy?