Apologies if this is deemed irrelevant.
As a DIYer for over 50 years and now retired - and still "at it"! - I never cease to amaze how backward in some respects are the regulations in Britain vis-a-vis Germany where I lived and worked between 1998 and 2003.
I "curse" every time it becomes necessary to carry out that child-like level of maintenance associated with changing the washer on a "bog standard" pillar tap. After all, it "aint" rocket science: any very basic DIY book will describe correctly how to do it - unless it is printed in China(:=D) - and for the record, who invented today's modern plumbing systems in the first place anyway?
Without fail it has been necessary, every time I have had to change a washer, to completely shut down the water supply for the entire house so I could remove the necessary components from the tap header to enable me to fit a new washer. "If" all goes well it takes about 15 minutes! But if it doesn't go well: the tap may have performed adequately for several years and you find trying to separate the header turns out to be a "nightmare". You find your [normally] adequate tool-kit is now useless and you have to either consider "popping" into town ( half an hour's drive away) to buy a more robust tool or try and borrow one from "somewhere" or "someone".
Four hours later the wife is screaming at you; she needs to have a bath or bath the kids who are also "dying of thirst" and you are at your wits wondering if you're ever going to get the tap apart!
How much simpler it would be if every water outlet in the house was locally isolatable fron the mains via a check valve - exactly in the manner cisterns are required by the water board so to be. Why stop short at just the lavatory cisterns? In Germany they simply do not quibble and have made it a statuatory requirement to fit isolating check valves - hot and cold - to every point from where water can be drawn off. Changing a tap washer shouldn't invlove shutting down the entire supply to the house - it's ludicrous, but the dear old, stiff upper lip, Brits do it without complaint - or do they?: in a large family unit it can be a major upset especially if the process of changing the washer on a single tap doesn't go "according to plan" and too often in my experience, which is engineering based via a toolmaking apprenticeship, often doesn't!
Does anyone know (or care?) why Britain is so behind the Germans in this respect and why we must suffer this mindless decision ( by who-so-ever) to allow sanitary installations to exist without the benefit of locally sited isolating valves? Please don't tell me it's cost driven: all the builder has to do is factor it into the house price. And what does it really cost at 'first fix' level to install a valve costing "all of £5" retail and that's tops? (£40 - 50 retail - at the most - for a mid-priced detached house with three "wet rooms").
Faced with this task at close on 70 years of age after moving into my new, downsized, house - albeit with three wet rooms, which includes a ground floor 'loo' - I wilted: retro-fitting anything in a house that is lived in is always a "big ask" and getting a plumber to carry out standard repairs is hard enough as it is - getting a plumber in to do a 'major' retro-fit ? ....nigh on impossible; unless you are prepared to pay a premium!