Depending on your location, you would have to balance storage amount to last between rains, and as the storage gets bigger it gets extremely heavy. (A 50 gal drum of water is over 400 lbs, or ~190kg) A pump you have to service/replace every few years is way easier to deal with than trying to set up a structure to safely hold hundreds of kilos/pounds over your head in a place where leaks could mean heavy water damage to the house.

There are small 50 liter hot water tanks that hang on the wall. There are just two bolts going into brick. When I first saw that, I was suprised that it was safe to do but it is in fact how they are meant to be installed. I think these are even bigger than 50L:

If someone is uncomfortable with the factory design, there is this aftermarket mounting system that uses 4 bolts:

People throw away hot water tanks like this all the time, which I thought could be repurposed for rain harvesting. All my cisterns have two inputs, left and right, depending on where the pipework is. And they are already connected to tap water with a valve. So I could easily pipe rain water to the unused cistern input and turn off the tap valve, and turn the tap valve on if the reservoir is empty. I guess gravity fed water would be slow to fill, but probably fast enough if there aren’t many users.

I was thinking I could cut a hole in the top of an old tank for the input then on the top side have an overflow hole near the top that feeds the downspout.

Indeed I do the same. Clean acid to descale kitchen appliances, usually muliple times. Then that gets recycled for dirty (bathroom) jobs. Though the kettle cleaning acids tend to be weak, I think. Vinegar is not potent enough for tough jobs. And I probably would not try hydrochloric acid in metal kettles.

I wonder if it makes sense to mix recycled vinegar with hydrochloric acid in a toilet – or whether that’s playing with fire.

Citric acid is less commonly available, but since you say it can work in metal kettles and also the toilet, it piques my interest… I’ll have to consider tracking some down.

This sounds interesting. It makes me wonder why no cisterns already have built-in softeners.

OTOH, if I am willing to accept the extra home improvement effort and complexity anyway, I wonder if I am better off harvesting rainwater, which I presume is soft water. A friend does this. After flushing, we hear a pump turn on to pump water from the rain reservoir to the cistern. A pump does not appeal to me, but I wonder if I could do a ceiling mounted reservoir on the top floor and then rely on gravity to feed the cisterns.

well, not sure how that helps. When the showerpan flexes, the drain still moves. And if the drain is an elbow fitting, I would think it’s harder to manage the movement when it’s a horizontal pipe moving vertically. The accordian pipe should work with that, but if the drain is vertical then I think i have a choice between accordian piping or rigid.

Nonetheless, thanks for the suggestion.

(update) someone mentioned that the drain is probably not moving only vertically… it would be moving outward, both vertically and horizontally. So apparently a hack would need to use an accordian style pipe.

I have seen those blocks of something that go either in the cistern or hang under the rim. I was never quite sure if they were for aroma, disinfecting, or if they did something to control limescale.

I don’t suppose they would all be created equal. Guess I need to look into it.

That was one of my questions. I am looking for min effort. If a quick brushing simply prevents the limescale, that would be less time and effort. But if limescale would still build up anyway, then I would not be interested as it would just add to the big effort every few yrs.