I've mentioned this before and it happened decades ago, but it was over a year before my mother discovered our "mains" water tap in the kitchen was actually fed from the cold water tank in the loft.
It was the pigeon feathers coming out of the tap that did it.
On inspection there was a least one dead bird floating in the tank and a whole lot more stuff besides.
The tank was original (and huge with 8ft sides) and the attic room wall had been built around it.
The house was built in 1870.
The water supply pipe to the house and tank was 2" iron but the pipe running down from the tank to the kitchen tap was lead!
I've got a water softener here, which I moved from my previous house down in Hampshire.
It works well - costs a bit in salt, but the softened water stops my daughter getting problems with eczema, so well worth it. The rest of us really noticed how much softer our skin was once the softener went in - my hands used to dry out to the point where the skin would crack & bleed, now I get very few problems. I wouldn't want to drink the softened water - quite apart from any health issues of the sodium content, it does taste a bit "brackish". Fine for brushing your teeth, but the supply to the kitchen tap for both drinking and cooking purposes is hard water.
Due to the vagaries of the plumbing here at Feltwell Towers, we still have hard water going to the dishwasher and washing machine, when it would be much better being softened water - No. 1,587 on the list of things to do.......
We also had a lead supply pipe, but due to the hard water I wasn't overly bothered, it had about 80 year's worth of limescale coating the inside of it. Water softener made no odds as it's connected after the lead supply pipe. However, as we were digging our driveway up anyway and I wanted to put a water supply into my garage, I took the opportunity to replace it with a new blue plastic pipe - much easier to connect to.