Drip Drop Water Talk

Separating the sales pitch from science

Category: Q and A

Factors that Contribute to Drinking Water Quality

factors affecting water quality

 

Q: What factors contribute to the quality of a city’s drinking water?  It appears according to a recent report, 10 U.S. cities with the worst drinking water, that Florida has two cities which show up on the list (Jacksonville and Pensacola). For a peninsula, you would think the quality would be better. How does the natural Floridan aquifer affect the quality of the water (other than providing a sandy taste)?

 

A: The two biggest factors that contribute to the quality of a city’s drinking water are 1) the source of the water and 2) what treatment methods are employed before sending the water out.

Jacksonville has a lot of disinfection by-products in the water.  It’s hot there and biological contaminants will grow pretty easily in the water so the city uses disinfectants such as chlorine to reduce the growth of microorganisms.  The chlorine will react with organic matter that is present in nearly all water systems to produce disinfection by products.  According to Jacksonville’s website their water comes from a limestone aquifer so the source of water isn’t bad, they just use chlorine to keep biological contaminants out.

Pensacola has the deck stacked against them with their source water.  There the water comes from 32 sand and gravel aquifers, which many organic contaminants can easily leach through to get into the water table.  The water utility tries to clean up the water with a lot of adsorption media but it’s expensive to treat a lot of water that’s going to be used in toilets and for watering your lawn.

 

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Reverse Osmosis and Bacteria

Do reverse osmosis filters remove bacteria-

Q: Do reverse osmosis filters remove bacteria?  How?

A: Yes, bacteria will be removed via reverse osmosis due to size exclusion (i.e. the bacteria are larger than the pores in the reverse osmosis membrane so they can’t pass through).  However there can be defects in the membranes which allow the bacteria to pass through.  I’ve also seen it hypothesized that the bacteria will move around the o-ring which typically seals the reverse osmosis into place within its housing.  Secondary contamination, where bacteria will move up the pure water stream and attach to the membrane, is also a possibility.  This is why while bacteria can be removed via reverse osmosis, these systems are rarely certified to be microbiological purifiers.

 

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