The following is based on a Water Technology "Technical Feature" (March 2010) by Rich DiPaolo.

“Depending on the location, this ranges from 1,000 TDS, which is considered the beginning of brackish water, to the neighborhood of 10,000-12,000 TDS, which we refer to as higher salinity and higher brackish,” explains Kevin Terrasi, vice president of engineering for Pump Engineering and ERI Company.

The basic process of treating brackish water in desalination applications is to pass pressurized water through a membrane. As fresh water passes through, brine or wastewater is rejected.

“The difference between seawater applications and brackish water applications is the level of the osmotic pressure required to achieve fresh water,” notes Terrasi.

Typically, the pressure needed ranges in brackish water treatment from 5 psi to 75 psi, although the majority of brackish applications fall in the 145 psi to 290 psi range.

Brackish water is generally a surface-type water and as such can be influenced by such environmental factors as rainfall and humidity.

As a result, advises Sammy Farag from AMPAC USA, be mindful of seasonal trends and record findings.

“For example, ion levels and bacteria could be higher in the summer months compared to winter months,” says Farag, who adds that salinity, nitrates, iron, silica and bacteria are a few examples of what is common in untreated brackish water.

An inability to identify what is in brackish water can lead to problems. For instance, if too much silica is present, passages, membranes and filters can become clogged, hindering the system’s performance. Moreover, if high nitrate levels are present, the system can become contaminated and foul membranes.

“The main thing is — before you touch this application — to make sure that you get a [proper] water analysis so that you don’t get any surprises,” asserts Farag. “For any reverse osmosis system, the pre-treatment [must be] built accordingly to specs of the water analysis. If it is not, then you will face tremendous difficulties.”

And because brackish water can vary in its makeup, different solutions will be needed. For instance, a high level of ion should be answered with greensand filters or oxidation as a pre-treatment.

In addition to troubleshooting based on inspection, brackish water also presents operational challenges as well. Pressure ranges can vary and affect the success of properly treating brackish water.

Technology to treat brackish water continues to improve and it will be even more crucial in coming years as our dependence on all water sources will continue to grow.

Today, brackish water treatment is commonly being used for a variety of new reasons, such as for our military, vegetation and to answer the need of sustainable, smart water usage where practical.

According to the Wikipedia:

Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salten" or "salty". Certain human activities can produce brackish water, in particular certain civil engineering projects such as dikes and the flooding of coastal marshland to produce brackish water pools for freshwater prawn farming. Brackish water is also the primary waste product of the salinity gradient power process. Because brackish water is hostile to the growth of most terrestrial plant species, without appropriate management it is damaging to the environment (see article on shrimp farms).

Technically, brackish water contains between 0.5 and 30 grams of salt per litre—more often expressed as 0.5 to 30 parts per thousand (ppt or ‰). Thus, brackish covers a range of salinity regimes and is not considered a precisely defined condition. It is characteristic of many brackish surface waters that their salinity can vary considerably over space and/or time.