An all Bermudian water engineering company is bringing technology to the island through a process called Reverse Osmosis.

The Royal Gazette <$>recently spoke with R. Ian Saunders, President of Carapace Consulting Services Ltd who explained what Reverse Osmosis is and why we use it.

What is Reverse Osmosis (RO) and what has it done for the Island’s water supply>

RO is a form of water treatment using membrane technology. In Bermuda, at its two extremes, it is used to process seawater into drinking quality water and is used to process drinking quality water into near pure water, H2O.

Without RO, Bermuda would not be able to meet its current demand for drinking water. Most large hotels have RO plants and hundreds of companies and individuals have RO plants to meet their supplementary water needs. Many hundreds more have drinking water RO units. Some Bermudians may not have a water main in the area, have had difficulty in securing trucked water supplies, not like the taste of delivered water, or may simply wish to be independent and can afford to do so.

Some Bermuda residents do not appear to be as water conservation minded today as those in past years and although still practicing water conservation techniques, many residents are now being housed in apartments and house conversions where the shared roof catchment area is insufficient to collect enough rainwater to meet basic requirements for today’s living standards. RO makes up the shortfall.

How does RO work?

The groundwater, mains water or tank water that is to be treated by RO is first filtered to remove large debris and any residual chlorine that may be in the water. The filtered water is then pressurised into an appropriate semi-permeable membrane. The membrane is a molecular scale filter. To work, the membrane must be able to continuously flush the surface of the membrane to remove the unwanted molecules, dirt and debris. The proportion of good water (permeate) to the waste water (concentrate) varies depending upon the system design. The least efficient systems have a 10% recovery, (Ten gallons supplied to RO, yielding just one gallon of permeate) and the best, around 80% recovery. Recovery rates are a factor of feed water characteristics and design. The disposal of waste water for small systems can be to the household cesspit or a soak-away. For larger systems, waste is usually discharged to deep sealed borehole as advised by the Environmental Authority.

B>

You said there are two types of RO, could you explain the difference between the two?

To better explain what the two basic types are, one needs to understand some very basic water characteristics. The quality of a water can be described by using Total Dissolved Solids (TDS), in parts per million (ppm). Very basically, the higher the TDS, the saltier the water.

[bul] Seawater is around 36,000 ppm TDS.

[bul] Groundwater in Bermuda can be between 300 and 36,000 ppm TDS depending upon location.

[bul] The Department of Health’s Drinking Water Standard is 800 ppm TDS.

[bul] Drinking water supplied by Bermuda Waterworks and Government water mains is usually around 500 ppm TDS.

[bul] Residential water tank (rain), depending upon location, is around 100 ppm TDS.

[bul] Bottled water TDS is highly variable and can have very high TDS values, so read the labels.

[bul] Pure Water is 0 ppm TDS.

Groundwater, which is unsafe for human consumption until treated and disinfected, is treated by RO to provide additional quantities of drinking water. The other type of RO is used to treat what is already considered to be drinking quality water.

Groundwater RO systems are broadly divided into three types based upon the TDS of the feed water. Seawater, Brackish and Fresh RO’s.

A seawater system will generally be required for a TDS in excess of 10,000 ppm. A brackish system for a TDS in excess of 1,500 ppm and a fresh system for groundwater up to 1,500 ppm TDS. All will process the different salinity water and produce water that is of drinking quality.

How do you decide if you need an RO pla<$>

A: A groundwater RO plant can be very expensive to own. Several factors should be considered before any decision to purchase is made.

1. Review your household water usage to determine if you can use less water whilst maintaining the standard and quality of living you desire.

2. Check to make sure that your tank is watertight. You may have plenty of water and are just losing it to leaks. Testing is simple.

3. Regularly check that the roof rainwater leaders are clean, so all water is collected.

4. Check and fix leaking valves, pipes and taps.

5. Calculate your regular shortfall in water supply. It is less costly to buy a couple of thousand gallons of trucked water every month than it is to buy, operate and maintain an RO system.

6. Can you collect any additional rainwater.

7. Determine what you want to use the additional water for.

8. Consider groundwater for toilet flushing and laundry use if low salinity. (Toilet flushing can account for 30 percent of household water use.)

9. Consider connecting to either a Bermuda Waterworks or a Government water main. This is frequently the least problematic solution for meeting supplementary water needs.

If there is no other less costly way to secure a regular and reliable supply of supplementary water, you may need an RO plant. Match the RO plant size to meet the supply requirements because RO plants work best when run continuously and must at least be operated frequently, irrespective of water need.

How does RO affect the residential u?<$>

A residential RO system will enable the homeowner to do whatever they wish with water.

Extended showers, always Extended showers, always flushing the toilet, water features in the garden, a swimming pool. The wish list becomes endless.

How economical is RO?

Groundwater RO plants and their associated abstraction well and pump, pre-filtration and post treatment disinfection, controls and waste disposal systems are relatively expensive to buy, install, operate and maintain. Before committing to an RO system, make sure you know the system life costs.

With groundwater RO plants, the higher the TDS of the feed water, the higher the cost of the equipment. A fresh water RO plant may operate at 100 pounds per square inch of pressure (psi), while a seawater RO plant will require between 800 and 1,000 psi of pressure. Pressure costs money.

Although seawater systems require higher operating pressures, fresh and brackish waters are more likely to have microbiological contaminants, which can make them more challenging to operate successfully.

The production capacity in gallons per day (gpd) of an RO plant will also influence cost. The more capacity, the more money it will cost. Small fresh water RO systems will likely cost a couple of thousand dollars to install, excluding the abstraction well construction, while the same sized seawater RO system will be several thousand dollars.

Unless you are able to undertake preventative maintenance and servicing yourself, monthly servicing by a reputable company will likely cost a minimum of $100 with repairs and replacements in addition to this.

Small under-the-sink (UTS) drinking water RO plants are less costly to install and can operate satisfactorily for several months between services. The water produced is nominally less costly than bottled was.

How environmentally friendly is it to run the RO plant?

This question needs to be separated for the two basic types of RO and it should be remembered that before any decision is made to purchase and install an RO plant, all options should be considered and evaluated from an economical and environmental point of view.

GroundwateO: <$>Where there is a proven need for supplementary water and where treating by RO is considered the most practical and cost effective option for securing the additional supply of water, it is likely that an on-site RO plant would also be the most environmental friendly selection. There are of course many variables and each application will have different factors to consider.

Drinking water RO: Where water is already considered to be of drinking water quality, it cannot be considered to be environmentally friendly to further treat it with RO. Treatment requires power and most small drinking water RO plants are extremely inefficient users of water. For every one gallon of high quality water produced, up to nine gallons of otherwise good drinking water is usually flushed to waste.

In the vast majority of cases there is a belief that tank water is unsafe, which is usually unfounded where reasonable precautions and recommended maintenance is undertaken. Where the concern over tank water is a taste/odour issue, these can be resolved by the use of combined sediment and carbon filtration.

For peace of mind, ultraviolet disinfection will ensure that the water is microbiologically safe. These filtration-UV lamp systems do not waste any water, use house pump pressure and only enough electrical power to light thamp.

How many RO plants are on the Island?

In all categories, small through large RO plants, there are probably in excess of a 1,000 operating RO plants on the island.

According to a Government report, the Island uses 5 million gallons of water per day. How much of that is from the RO plants?

It is believed that most residents remain self sufficient in their water needs by using just their rainwater supply, with or without the assistance of a domestic well for flushing water.

Others, including our hotel visitors, require supplementary water that is delivered by on-site RO plants, water truckers or water mains.

I would suggest that close to half of all water currently consumed in Bermuda is now derived from RO.