Sharing. It’s a good thing in a household. Take the bath water. Now, I am an inveterate bath-taker, which I know is not an environmentally sound thing to be, but, alongside this, I am an ardent bath-sharer, which is environmentally fantastic. It doesn’t seem right, somehow, to run a fabulously hot, deep bath, lie in it for half an hour, then run it all away. So, I have devised a special signal for Mr Millard, which calls him to his bath. It’s a sort of high-pitched yoo-hoo that works as well in a domestic setting as it would on a crowded street. When he materialises, I jump out and he jumps in. He likes tepid water, and I’m never that dirty, so the arrangement pleases us both.

I grew up sharing bath water. I suspect it took off during the war, when children would double up in order to save on heating bills. This habit was passed down by these wartime children to their offspring (my generation), who are still sturdily continuing to share their bath water, even though we are more than 60 years away from the last threat to British sovereignty.

Indeed, a little research suggests that we fortysomethings are the last of a once thriving group who are prepared to get wet communally. When I asked anyone younger (or a bit older) if they, too, enjoyed this conspicuously green habit, there was one response: “Yuck!” My niece, who, naturally, has been brought up in a similarly communal household as far as baths go, was asked this week in class whether anyone shared their bath water. On noticing that not one single other person put her hand up, she kept hers down. Sharing has, effectively, leaked away from the bathrooms of the nation.

It seems people are essentially too nervous to get into another person’s bath, even if that person is their parent, sibling or significant other. Worries about coming into contact with stray toenails, germs and other unmentionables mean that, even though the idea of sharing water has been proposed by Newsnight’s former Ethical Man, Justin Rowlatt, and by countless global-warming information booklets, it just isn’t catching on in the same way that, say, recycling is.

Yet why not? It’s a good thing. It saves on heating costs, saves water, saves time (no hanging around waiting for a fresh bath to run) and is generally quite a friendly thing to do.

If you are fantastically ecologically minded, you can even invest in a “grey water” diversion kit, which will send your used bath water pouring onto your rose bed outside. A company called Ecoplay has devised a rather Heath Robinsonesque machine to divert your bath water into the loo cistern, while my local council, Islington, urges us to save our grey water and recycle it, apparently via the use of a bucket. Okay, it might mean lugging gallons of water around the house, but just think what that will do to your upper-arm tone.

Once you’ve started sharing your bath water, you’ll find there is no end to the things you can get up to in the world of domestic sharing. It’s about time we thought about it. According to the Town and Country Planning Association, the rise in the number of single-occupancy households is a significant reason for the shortage of housing in this country. In the UK, 31% of households have a single occupier, but this figure is growing fast, and will soon match countries such as Germany (37%) and Sweden (46%). So, why not share your house?

Taking in a lodger is a brilliant way to earn a bit of extra cash. Under the rent-a-room scheme, you can earn up to £4,250 a year, or a little more than £350 a month, tax-free. It is not as onerous an undertaking as having a tenant, because lodgers do not have security of tenure. They can’t swan around and call your place their own, because it’s not. It’s not an invitation to communal living, either. If you give them notice to leave, they have to. You don’t even have to be the homeowner, although, if you are renting, you need permission from your landlord before you welcome in a lodger. Legally, you don’t have to draw up a formal agreement, but it’s a good idea, as is setting up a direct debit for the rent.

Before our bedrooms were overrun with offspring, we had a sequence of charming lodgers, most of whom worked for the Today programme. It was rather exciting; they would appear, eat some toast and Marmite, mumble something about interviewing prostitutes, or MPs, or sometimes both, and disappear in the direction of Broadcasting House for 36 hours. Then they would reappear, talking excitedly about what John Humphrys is like at 4am. (Imagine what you will, then quadruple it.)

The good ones used to provide cases of red wine at regular intervals and make the occasional cup of tea. The not so good ones left dirty clothes lying around. In either case, their presence was highly beneficial – in terms of the reduced argument count between Mr M and myself, and of our bank balance. We never had to sling anyone out, or start reading the Riot Act. I don’t think I offered my bath water to the lodgers, but, given time, it would have been a treat in store.

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