Structure

The Portsmouth area is well-blessed with water. Clearly, its wealth has historically depended on its well-protected harbour, but its supply of freshwater is another significant favourable factor.

Portsmouth has always had access to abundant freshwater, because of the great aquifer of the Chalk South Downs to its north. Portsdown Hill is a key component of the geological structure which concentrates the emergent water from this large catchment area.

Natural Springs

As late as 1925, the city's needs were supplied only by springs, which were sufficient for the populace environs: "Even at the end of the long draught of 1921, when many other water undertakings were obliged to restrict their services for a long period, the natural yield was more than sufficient to meet all requirements". These were the springs at Havant and Bedhampton; and had surplus water over and above that needed to supply "about 270,000 people".
A major factor was the geological conditions, which meant that water from drainage from an extensive tract of country converges at the surface within a very restricted area; so these springs produced a huge volume of freshwater.

Geological structure

The Chalk of the South Downs is the main aquifer of supply, with Portsdown playing a key role.

In the Portsmouth area, the chalk rocks have a general gentle southward dip, from the South Downs under Portsmouth, then re-emerging in the Isle of Wight. Between, the chalk is overlain by London Clay and Reading beds, which provide a seal over the porous chalk. However; between the South Downs and the Isle of Wight, the Portsdown anticline, although small, has a profound effect on the underground water flow.

Although the actual emergent ridge is only 7miles [ km] long, stretching from Fareham to Bedhampton, its axis continues further eastwards, past the site of the springs. (However, there are no topographic features to mark it east of Bedhampton, as its arch has been eroded to nearly sea level).
This chalk is both porous and permeable, allowing it free water movement.

Porous means it has spaces, both pores and cracks; permeable means these are joined, allowing movement.
Pumice is porous as it has many holes from gas-bubbles; but these are all sealed from their neighbours, so fluids cannot flow, so it is not permeable.
A reservoir, for water, oil or gas, must be both porous and permeable, and have an overlying seal of impermeable strata. It must also have a structure that traps the fluid in the porous rock, below the seal.

Not only does the water's porosity allow underground movement, it also prevents streams existing above ground; as rainwater simply soaks into the underlying rock.

The overlying Reading Beds however, are a thick stratum of impervious clay, providing an absolute seal that prevents water leakage. This clay is one of the major factors that determine the points of emergence of the underground water.

The underground water system

The general trend of water movement is southwards, from the main source of water in the South Downs, towards the Solent. (If water from the Portsmouth Chalk contributes at all, it is only to a small degree.)

As rain falls on the Chalk, it soaks downwards through near-vertical cracks, until it reaches the level where the chalk is already saturated (as there must be a base to the permeable strata, which in this case is the underlying Selbourne Beds of [[ ]]. From here, it drains along the 'path of least resistance', to lower levels, which is mainly southwards under the Tertiary beds, following the dip of the strata.

However, meeting the Portsdown anticline, it cannot continue its southerly course [[why not??]], and is deflected around the east end (where it emerges as springs in Fareham) and the west end, supplying the in Bedhampton and Havant. The majority of the water deflects west, emerging in a number of places within a 1-km-radius in an irregular line, known as a 'spring line', roughly parallel with the edge of the tertiary outcrop.

The water that emerges, whatever the season, is at a constant temperature (51ºF, 10.5ºC) [1925], indicating a deep-seated origin, insulated from the seasonal variations. This offers a practical advantage, in that it is relatively cool in summer, and warm in winter. This is desirable for domestic use, so advantageous for energy-consumption when the water is cooled, or heated, to the desired temperature.
It also reduces the chances of ice trouble in frosty weather, although there is still possibility of this.

The yield of these springs is relatively constant, due to the equalising effect of the natural storage in the Downs. However, the yield is noticeably seasonally dependent on rainfall. The lag is around a month; meaning that a heavy rainfall results in higher yields about a month later. Peak yields thus occur in early spring after high winter rainfalls, and shortages from dry conditions are only felt a month later.

Current Supplies

In 1925, the springs at Bedhampton and Havant supplied sufficient water for the whole of the Portsmouth areas, with some to spare. Now, with growing needs and population, Portsmouth Water cannot rely on just these springs, but also abstracts water from wells and boreholes in the chalk, as well as from the River Itchen to the west. Furthermore, water is stored in 35 underground reservoirs, including [[3][check]] on Portsdown Chalk, at Southwick, Nelson and the George.

Portsmouth Water supply water to….
Southern Water are responsible for….
Consequently, Residents of the Portsmouth areas receive bills from both Southern, and Portsmouth, water companies.

Portsmouth Water currently supplies over 289,000 domestic and commercial properties in South East Hampshire and West Sussex.
For examples: in the year 2001/2002 67,658 million litres were abstracted, from:

The 55% from wells and boreholes comes from over 20 sources.
Clearly, 85% of local water is still the groundwater from within the chalk.

Water Quality and Hardness

The water from the chalk aquifer is of high quality, and requires only minimal treatment at most sources. It is well known in the area that it is 'hard water', so it does not lather well, leaves 'scumming marks' in the bath and on glassware, and furs-up kettles and shower-heads. This 'fur' or scale is calcium carbonate (CaCO₃), which is chemically identical to chalk. As the water passes through the rock, calcium carbonate dissolves into it, then later precipitates out, depending on the conditions.

Water Hardness

Hardness in water is mainly due to the presence of ions of calcium, magnesium and iron, while their balancing 'anions' may be either carbonate, sulphate, chloride or nitrates. Obviously, the salts in the water depend on the rock type of the areas through which the groundwater percolates.

If the anion is bicarbonate, as it is in Portsmouth, the water has "temporary hardness": heating it above 70ºC causes the carbonate salts to precipitate out - giving scale and soft water.
The "permanent hardness" given by sulphate, chloride or nitrate salts cannot be removed by boiling.

Hard water in Britain tends to follow a north to south-east gradient, with the softest water in Scotland and northern England and the hardest in East Anglia and south-east England. In the north it percolates through granite, while in the south and east, through chalk. Hard rock (granite) is difficult to dissolve, so the water is soft; while soft rock (chalk) is more easily dissolved into groundwater, so giving hard water.

Despite the inconvenience of hard water, it has the advantages of taste, and health benefits.

Health Aspects

Within Britain, mortality from cardio-vascular disease (i.e. heart disease and strokes) tends to follow the same pattern as soft water, with higher rates in the soft-water areas of the north and lower rates in the hard-water south and eastern areas. The effect is statistically significant, even after adjustment for socio-economic and climatic factors.

It has been shown that in towns with very soft water, with CaCO₃ below 25mg per litre, the cardio-vascular mortality rate is 10-15% higher than in area with high concentrations of CaCO₃ (above 170mg per litre). It has been shown that there is no difference above that level, of 170mg per litre; but hardness up to that level is clearly beneficial.

For this reason, water-softeners cannot, by EC law, reduce water hardness of drinking water to below 150mg per litre, where softeners are used. However, many areas have levels way below that, and suffer from it.
In Portsmouth, we have some of the hardest water in the country, with the CaCO₃ level at [[ what?? ]]

Lead Protection

As cities, and the consequent demand for fresh water grew, many miles of piping was laid under the ground, for mains, service-pipes and domestic pipes on private land.
From Roman times onwards, lead piping was used, while mains were made almost entirely of wood up until the 18^th century. From the industrial revolution on, cast iron was used for the larger pipes, with Edinburgh replacing all of its lead mains water pipes as early as 1755. Today, where pipes are replaced, PVC or polyethylene is used.
However, much lead piping still exists, supplying domestic water around the country.

We now know that the water flowing through lead pipes collects particulate lead, which is carried to the user; and when ingested leads to (mainly neurological) lead-based diseases. (Recognition of lead poisoning from the atmosphere was the main reason that leaded petrol for cars was phased out in the 1990's).

Old cities, including Portsmouth, still have lead piping, mainly in service pipes supplying, and private piping within, pre-1970's properties - although efforts are being taken to replace them. Where this is not possible, 'acid dosing' of the water is being practiced, which forms a seal on the inside of the pipe, which prevents lead dissolving.
In recognition of the health problems of lead, EU directives include stringent targets to limit lead content of water (from 25 mg/litre in 2003, to 10 mg/litre in 2013).
Portsmouth met the 2013 target by 2002, although traces of lead can still be detected in places.

However; even before these measures, Portsmouth has suffered less from lead poisoning than many other cities did, courtesy of their hard water. As 'hard water' currently furs-up our kettles, the calcium carbonate from water precipitated a layer onto the inside of the lead pipes, effectively sealing much of the lead away from the water.

The fur we curse today has historically protected the populace from the worst of lead poisoning from its water supply, as well as from cardio-vascular disease.

For any comments, suggestions or contributions, please e-mail me at: portsdown@bbm.me.uk

Water from Beneath the rocks