---

Dear Sir,

Rowan Hallett's article entitled 'Making saltwater drinkable could leave a sour legacy' is wide of the mark and I feel compelled to respond.

Let us begin with the image of the seawater desalination plant polluting our surrounding ocean with its own "by-product" or "reject" water leading to an increase in ocean salinity long term that turns our fragile underwater ecosystem into a "dead sea" where the salinity rises, and all else "collapses." To make such a statement and to go on and state that future generations may never enjoy the pleasures of snorkelling or whale watching, totally ignores the "hydrologic cycle."

The hydrologic cycle describes the processes by which water evaporates from the surfaces of the earth and oceans, rises through the atmosphere, cools, and condenses into water droplets (clouds) and then returns to land and oceans as rainfall. One of the fundamental laws of conventional chemistry (non-nuclear) is that matter is neither created nor destroyed. The earth has a finite quantity of water in three states, solid ice, liquid water, and water vapour. The vast majority of our water is not fit for human consumption in its natural state because of its chemical and/or microbiological content.

To suggest that a seawater desalination plant is going to induce a rise in salinity in the world's oceans to create a dead sea is to take a myopic view of naturally recurring events. It is true that a seawater reverse osmosis plant does have a reject hyper saline water stream.

It is also true that if this hyper saline reject were just permitted to be discharged back into the ocean through an open pipe it would create a plume of saline water that would adversely affect the ecosystem in its immediate vicinity. However, no one dumps hyper saline reject water directly into the ocean. The environmental authorities simply would not allow it. Any hyper saline reject water discharge would have to be designed so that there was minimal to nil environmental impact from the discharge.

Nozzles on the seabed

A common method of dispersing the hyper saline reject is to have a number of nozzles a distance off the sea bottom aimed at a 45-degree angle up into open water. The nozzle sprays out the hyper saline water on a trajectory that takes it up and out into the water column at a high velocity, causing rapid mixing in the surrounding water. The salinity profile rapidly returns to that of normal seawater within a short distance from the discharge nozzle.

Remember the hydrologic cycle. Somewhere it is raining very low salinity water back into the ocean or a river is emptying its fresh water into the ocean. In the context of Bermuda, when it rains, a percentage is collected off our roofs that ultimately goes into a septic tank and drains to sea level either to recharge an underground lens or directly mix with sea water; another percentage percolates through the ground to sea level to recharge underground lenses or mixes with sea water depending on the geology; another percentage runs directly off to the sea and another percentage evaporates back into the atmosphere. Overall there remains a conservation of water, it is neither created nor destroyed. Overall, on a small platform in the middle of the Atlantic Ocean, you are not going to see a change to our ecosystem because of a seawater RO plant operating long term.

Bermuda Waterworks has been operating a seawater RO plant for almost 15 years with a reject stream discharge through a series of nozzles as previously described. Where it discharges there are sea grasses growing that require salinities less than normal seawater. The grasses grow and the seawater salinity is less than normal because of the outflow or leakage of our groundwater lens in Devonshire to the sea. This leakage is a natural necessary dynamic for the lens to exist and cleanse itself.

Monitoring

The seawater RO discharge after 15 years has not altered the salinity of the surrounding waters as attested by the continued growth of sea grasses. We continue to monitor seawater salinities in the vicinity and they remain substantially below the average salinity of seawater. This is actual life experience, the applied science works.

In short, seawater reverse osmosis plants that are discharging reject hyper saline water back into the sea through a well designed system are sustainable, and will contribute to enhancing the quality of life by providing a high quality, reliable drinking water supply.

The resident and transient population of Bermuda has increased four-fold or more in the past 100 years. There is only a limited amount of roof and water catch area available to collect rainwater. This is unsatisfactory for public water supply. It is also not as sanitary as one may believe, because it is an "open system." Rainwater collection is at the mercy of airborne contaminants and of course other contaminants that may be on the roof or in the tank.

As our population has increased, the quantity of water needed has increased. Bermuda is unable to harvest sufficient rainwater to satisfy the life needs on the island. It is necessary to supplement natural rainwater supply with other sources of drinkable water. Through a process of natural development, the ground water resources of Bermuda were first developed and as the demand continued to grow with population, it has become necessary to turn to seawater desalination for additional supplies of drinking water. Population growth is the primary driver for water demand.

Turning to alternate methods of water production, advocating water from air devices is not the answer. This technology actually uses much more energy per gallon of water than advocates would have you believe. It is not as effective or "green" as it is presented to be. To say a dehumidifier cools is rubbish; it does the opposite because latent heat is released when water vapour is converted into liquid water. I hope no one thinks they can drink the water from a dehumidifier - it is an open system and therefore unsanitary.

Water catches are a throwback to a by-gone era: they only harvest a small fraction of our total annual water needs. The amount of land that would have to be dedicated to this purpose to satisfy our requirements today will never be available. There is a paradox with water catches - when you need it most during a drought it is of no help. Once the reservoir runs dry, if it does not rain it is useless. On the other hand, a seawater reverse osmosis plant supplements water supplies and enables public water supply to continue when reservoirs would otherwise dry up. A seawater RO plant is compact, it does not have a large footprint, and the cost to run is directly proportional to its production.

Public water supply, its sources, its methods of treatment, storage and distribution, linked with the demand side economics and conservation is multi-dimensional and complex.

If your columnist wants to argue about the vices of consumerism and greed run amok then she should do so - but she should support her argument with sound reasoning.

D.A. Rance,

Bermuda Waterworks Limited

[[In-content Ad]]

---