British taps: here’s why the hot & cold are separate

Ah, British taps. For most Brits, separate hot and cold taps (or faucets, if you’re visiting from the good old US of A) are a part of every day life. However, for many visitors to the UK, including those from continental Europe as well as America, they are simply baffling. Why on earth are they separate? How can you wash your hands comfortably in water that’s either scalding hot, or ice cold? In this article, we’ll go through the most common arguments.

1. British taps risk contaminating the mains

One of the most widespread explanations refers to the construction of British houses after the Second World War. British houses built after this period were typically equipped with a cold water storage cistern in the attic. One of the main purposes of this cistern is to supply the hot water cylinder.

Nowadays, such cisterns are subject to a number of strict regulations in order to protect the water from contamination. For example, they need to have a lid in order to prevent debris and rodents from getting inside, and they must have certain fittings which prevent the ingestion of insects (which could otherwise find their way inside via travelling up the overflow pipe).

However, these regulations weren’t always in place. Older cisterns often didn’t have a lid, and they were usually made out of galvanised steel, which would corrode. Insects, rodents and even errant birds in the loft space would occasionally find their way into the tank, drown, and contaminate the water – which would eventually be used as hot water for the taps. That’s why, in British homes, your family told you not to drink from the hot taps or the bathroom taps.

It is this risk of contamination which is frequently cited as the reason why British taps are separate. It is argued that, in mixer taps, the hot water – which cannot be guaranteed as safe to drink – would merge with cold water from the mains and contaminate it.

Flaws – the taps

However, there are a number of flaws with this argument. The cold water storage cistern usually supplies the cold water to the bathroom outlets as well as the hot. Thus, there wouldn’t be any contamination of the mains water when both hot and cold come from somewhere else.

Another reason against this explanation is the taps themselves. Many mixer taps have separate internal waterways, meaning that the hot and cold waters never come into contact with each other until they exit the tap, so there’s no chance they can mix. As for mixer taps which do blend the hot and cold water inside the tap body, they require non-return valves to be fitted to both the hot and cold supply pipes. Either way, there’s no chance for contamination of the mains.

The water pressure

The other argument against this explanation is the pressure difference between the hot and cold water. Cold water from the mains is at a much higher pressure than water from the hot water cylinder, which relies on gravity.

It is theoretically possible in a faulty mixer tap or a mixer tap without any non-return valves for hot water to be drawn back into the mains. However, what often happens in this situation is that the high pressure cold water displaces the low pressure hot water, and fills up the cold water cistern from its outlet pipe at the bottom. It’s a common complaint from residents who, after installing a new mixer valve, find that their cold water cistern overflows when they run the bath or take a shower. In other words, the hot and cold water should never be allowed to mix with the chance of the hot water flowing back into the mains regardless of possible contamination. That’s because when it does, it tends to make the cold water cistern overflow.

So while this argument has a logical premise, it doesn’t really stand up to scrutiny.

2. Tradition

So why are British taps separate then? The simplest explanation is probably the best one: tradition. Most British housing was built at least a hundred years ago. In fact, many properties are even older. This was a time when there was no running hot water, and certainly no central heating. Mixing valves didn’t exist, and there was no reason for them anyway: any taps or spouts were cold only. The only way to get hot water was to heat it in a pan or a kettle over a fire. Consequently, when domestic hot water systems were invented, they were added separately. Houses which were rebuilt after the war carried on this tradition.

So what about, for example, Germany, a country where mixer taps are in practically every bathroom? German houses don’t have cold water storage cisterns  – all taps including the hot ones are supplied by a mains-fed tank. This means that there is equal pressure on both hot and cold, so no chance of creating an overflowing water tank.

But perhaps the reason why German plumbers took so strongly to mixer taps may be because of the sheer destruction of German housing stock during the Second World War. After the war, one in five buildings were destroyed. In many cities, not a single house was spared. Thus, there came the opportunity not to carry on a tradition, but to start a new one.

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