As a child, growing up in a small town in south east England, the milkman was one of the most visible supporting players in our community’s life. Once or twice a week he’d show up early in the morning and you could often hear him before you saw him, driving up the road in his electric milkfloat stacked full of crates, as the glass milk bottles jiggled against each other with each slight bump in the road. The bottles were all identical, imperial pint-sized, and unlabelled. The only thing telling them apart was the colour of the foil cap which identified each bottle’s milk fat content.

Our family always ordered silver cap, which was full milk and had an inch or so of cream at the top. Rich, but not as rich as the gold cap milk which was almost sinfully decadent. From time to time, if we didn’t bring the milk in early enough the local birds would perforate the foil cap with their beaks and get at the cream. This irritated my father no end as he liked to invoke the paternal privilege of getting the first pour for his morning coffee.

It turns out that birds are lactose intolerant and that milk will give them diarrhea, but the cream has no lactose in it and so is a tasty energy-rich treat for them, as it was for my father. Even so only two species of birds, the blue tit and the robin, learned to drink the cream at the top of each pint. It seems that the birds first learned this many years ago when milk was delivered without the foil bottle cap. That protective innovation was introduced after World War I but in less than thirty years the trick of perforating the cap had spread across the entire blue tit population. Blue tits flock together for several months and the young birds evidently learn from their elders. Male robins, however, are fiercely territorial and will shoo away others if they get too close. So even though some individual robins did learn the cap perforation trick it never got passed on from bird to bird.

For several decades the milkman was such a prominent feature of communities across the country that a whole genre of jokes grew up around him. More recently he and his electric milk float have gradually, though not totally, faded from view. But I am still struck by the very idea that milk can be delivered to our homes in standard sized bottles, and how that differs so dramatically from water delivery. When I want water I simply turn on a tap and out it pours in an undifferentiated, unmeasured flow. I can leave the tap on for as long as I like. I can water the plants, run a bath, wash the dishes, fill a kettle, and I can use a different amount every time without having to order it in advance.

As I think about this difference some more, it seems to me that nowadays mostly everything that we need to be delivered is done so like milk, in standard sized containers. This is obviously true of products like cereal or baked beans but also true of paper documents via FedEx envelopes, cars via sea containers, and digital content like emails, movies, songs and websites via the packet-switching network known as the internet.

In comparison, our experience of water delivery is actually rather rare and getting rarer. Apart from water itself, the only things that get delivered to us as a flow are electricity, radio and TV. Of these, radio and TV are being increasingly delivered digitally, over the internet, and are therefore now more like milk than water. Meanwhile, the traditional electrical grid concept of central power generation and always-on, use it or lose it electricity is being reinvented from all sides. The days of cheap and effective rechargeable batteries for home and car, linked to small scale power generation facilities like solar panels, potentially and intriguingly providing us with a hybrid water-milk delivery model that may even feed energy back to the grid, are hopefully not too far off. And that leaves us with water, which we inherit rather than make. We know how fortunate and few we are who have this precious flow at our disposal.

So when it comes to stuff that we want distributed, we seem to be leaving the world of water and embracing the world of milk. Technology transforms our experience of flow into episodes and transactions, bottles and crates, boxes and containers, envelopes and packets.

I’ve recently started to have milk delivered to our home again, after a break of at least three decades. It was a decision based on choice – it’s really good milk – rather than on necessity. The delivery mechanism remains more or less untouched, but many of the details of the experience have changed. We no longer pay the milkman directly but order and pay online. The milk bottles here in Chicago are US half gallon rather than imperial pint, and the bottle tops are no longer aluminum but plastic. And we never actually see or hear our milkman in person, though he does send his customers a holiday letter every year along with a photo of his family. No one tells milkman jokes anymore.