The Reason for Saline Underground Water be Saltier Than Seawater

Before the topic…You would think it would be impossible for underground water, which is far from the salty sea becoming salty too. But it's true; water can and often does become salty that it must be specially dealt with, even in places far inland, such as Arizona.

The salt content or salinity of water refers to the quantity of mineral constituents dissolved in the water and is generally reported as “dissolved-solids concentration.” It is measured and expressed as milligrams of dissolved salts in one liter of water [mg/L]. Water with less than 500 mg/L — about a quarter of a teaspoon of salts per gallon of water — is considered suitable for drinking and most uses.

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First, there is one kind of water that resembles sea water even though it is water inland. How is this? This type of water is called connate water, which is essentially sea water trapped on the landscape, and starts out with a salinity that is similar to sea water. Connate water that encounters highly soluble minerals such as halite (sodium chloride) or gypsum (calcium sulfate) can still dissolve a good portion of these minerals to become even saltier.

Fresh water originating from rainfall can become very saline ground water during a very long contact time (thousands of years) with easily dissolved minerals. However, the diversity of salts in these non-connate waters is much different from that of sea water.

The salts from both connate and non-connate possess their dangers as they flow with irrigation water and enter the soil. Where evapotranspiration (combined evaporation from soils and transpiration by plants) exceeds combined precipitation and irrigation, salts accumulate in the root zone. The water returning to the atmosphere is essentially distilled water, with salts remaining in surficial soils and in the root zones of plants. The salt accumulating near the surface of irrigated areas can damage and even kill vegetation.

The best solution to remedy the excessive salt is to leach the salts from the root zone by applying more irrigation water than evaporates. Excess water percolating through the root zone removes salts, and this deep percolation water, now carrying an increased salt load, continues downward toward the groundwater table. Along with salts, the deep percolation water also might carry residues of fertilizers and pesticides applied by farmers, grounds keepers and homeowners. This deep percolation water poses a threat to the groundwater quality beneath irrigated lands. Groundwater contaminated by deep-percolation water will eventually be too salty to drink or to irrigate crops or landscape vegetation.

Salty water eventually then finds its ways into wells. The salty water from wells can be disposed of in evaporation ponds or be desalted by reverse osmosis (RO) for reuse, including drinking. RO, however, produces a reject brine that must be disposed of. The salty groundwater and brine could be put in evaporation ponds. These ponds, however, not only require a lot of land but they eventually become environmental hazards. The volume of salty groundwater can be reduced by using the water to sequentially irrigate increasingly salt-tolerant crops, applying deep percolation water from one crop to irrigate the next more salt-tolerant crop, until it is used to irrigate halophytes that can grow in sea water. Salt is thus concentrated in a much smaller volume of water, for evaporation in smaller ponds.

If you thought that only sea water was home to salt then it's time to reevaluate your opinion. Water finds a way to eventually encounter many elements, nutrients, bacteria and more as it falls to the earth and finds its home amongst the land we live in. Salt is just one of the many things it encounters along the way.

Even with remarkable natural purification processes at work, it's a safe bet to keep the water you drink in your home safe with the use of a good water filtration system, especially as most city's water pipes continue to age and it is difficult for utilities to upgrade every component within a distribution system. Please visit the product page at to find out how to keep your water safe.

Read Next: Are Salt Levels in Drinking Water a Health Concern?

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