The perfect privy

The history of the toilet goes a long way to explaining why today’s plumbers must always keep backflow prevention top of mind.

AUTHOR: PLUMBERS, GASFITTERS AND DRAINLAYERS BOARD

It was in 1592 when Sir John Harington, godson of Queen Elizabeth I, invented the first flush toilet. His device was a water closet that had a cistern connected and could run water to flush the waste.

This invention didn’t really take off until the 19th century, when Thomas Crapper was commissioned to construct lavatories for several royal palaces. Crapper patented a number of toilet-related inventions based on Harington’s water-filled cistern idea, and that of watchmaker Alexander Cumming, who developed ‘S’ shaped pipes to stop foul odours coming back up drainpipes.

Great work BUT they inadvertently created another problem called crossconnection. This new flushing toilet directly connected the drinking water and foul water system, which was likely to cause deadly problems.

The issue was how to keep water drawn from the supply from re-entering it, and potentially being contaminated with the foul water from the drains.

The air gap is born

Not surprisingly somebody (probably a plumber) came up with the idea of having a gap between the water inlet and the overflow level in Crapper’s cistern.

Thus, the simplest form of backflow prevention, the air gap, was born—creating a physical disconnection between the water supply and a source of contamination.

The Romans had water and drainage systems previously, but the Industrial Revolution and Thomas Crapper’s new invention saw renewed interest in water distribution and waste removal systems. As a result, sanitary plumbing systems and inventions began to take off.

But it wasn’t until the 1930s that backflow and cross-connection issues hit the headlines, as the development of full-scale urban water reticulation systems combined with increasing numbers of high-rise buildings. Large numbers of deaths directly attributed to the contamination of the potable supply led to the need for some clear direction and laws.

This portrait of English courtier Sir John Harington, inventor of the first flush toilet, was painted around 1590 and is attributed to artist Hieronimo Custodis.

Formal industry standards

The first real thinking and formalising of industry standards for protecting water supplies began to take shape.

Potable water supplies to buildings in New Zealand must be protected and installed in a manner that avoids contamination both to the building in which they are installed and to the water supply that feeds them.

New Zealand Building Code Acceptable Solution G12/AS1 provides a means of

“A privie in perfection.” This illustration of Sir John Harington’s invention is from his 1596 book called A New Discourse of a Stale Subject Called the Metamorphosis of Ajax.

Supply flow

Diameter

Flood rim level Air gap, the greater of 25mm or 2 x Diameter

(a) Water tank with inlet pipe above flood level rim

Valve and float

Diameter Air gap, the greater of 25mm or 2 x Diameter

Overflow

Supply flow Sized to maintain air gap – outflow capability must be no less than maximum inflow

(b) Water tank with ball valve and overflow pipe below flood level rim

Above: Figure 1 in Acceptable Solution G12/AS1 demonstrates air gap separation.

evaluating the risk, selecting suitable control measures, and giving details for the general installation requirements of backflow prevention systems. Plumbers need to be competent in installing a device and also fully aware of how to identify the level of risk and apply the best means of control.

Compliance schedules

It is also important to remember that New Zealand buildings containing backflow prevention systems, other than single residential dwellings, are required under the Building Act to have compliance schedules. The compliance schedule requires that backflow prevention devices are tested on an annual basis before a warrant of fitness is issued for the building. In such cases, the plumber will need to make the building owners aware of this.

The testing of the backflow preventers must be done by an Independently Qualified Person (IQP), who is accepted by the territorial authority as being appropriately trained.

Just as Harington and Crapper put a lot of thought into creating their inventions, plumbers also need to put a lot of thought into what they are connecting to the water supply.

It is up to you, the plumber, to consider any existing or potential risk to the water supply and apply appropriate measures to ensure the water we drink stays potable and fit for human consumption. RHEEM.CO.NZ

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