A Cloud Comes with Every Silver Lining
Chris Salter, Los Cabos News, June 2009

The coarse 25 micron sediment filter shown below was taken from a La Paz Dentist’s Surgery after approximately 150 liters (40 gallons) of La Paz Municipal water had passed through it over a nine month period (a total of around 13,500 liters or 3,600 gallons or about 13.5 cu.M of water).

Why is the La Paz water so bad when it reaches our homes and businesses?  It certainly was not this contaminated when it left the pumping stations of the much-maligned and under-funded Water District facility.  The original water certainly contained a large amount of dissolved solids, including Calcium and Magnesium which is the stuff that causes all of the Scale problems in our household plumbing, appliances inc. the hot water boiler.  However, these contaminants will simply swim through this filter.  What you see here is trapped suspended contaminants including sand, silt, bacteria, etc.  We know that we must not drink this water, but after seeing this filter I wonder how many of us actually want to bath or shower in it!  How did these contaminants get there?

Well, in a perfect scenario, the La Paz Water District would like to be in a position to deliver around 400 liters (around 100 gallons) of water each and every day, to the 60,000 homes and small businesses in La Paz.  The daily consumption for a average 3 person family home in the USA is 225 gallons, but the average 4-5 person family homes in La Paz have been educated to be a lot more frugal with their water than their American counterparts.

This daily water consumption amounts to around 24 million liters or 6 million gallons per day, plus a chunk more for irrigation, agriculture, mining and other industrial demands.  Fine, they might even have that much.  However, when the water supply is turned on, around 40% is lost through leakage in the system.  This is probably to be expected as a City such as London, UK (pop. 8 million or so) with one on the best-funded and maintained water treatment systems and distribution trains in the world, also loses about 20% in leakage.

With this 40% level of leakage the La Paz Water District would have to deliver 40 million liters (10 million gallons) per day, without taking into account the other demands.…and this much water they certainly do not have.

Well, they came up with a really novel way of solving the problem.

They just turn on the water supply for a few hours each day and for a few days each week to fill up the underground storage tanks and/or roof-top Tinaco’s that come with each home and business.  They are probably still delivering somewhere near the daily 24 million liters (6 million gallons) consumer demand, but they have dramatically reduced the level of wastage to almost manageable proportions, as, during the many hours and days that they are not delivering, there is no wastage.

Let nobody say these water engineers are anything but innovative.

Unfortunately, with every silver lining there comes a cloud.  When the supply line is turned off, the pressure in the supply pipes also quickly dissipates.  Now this pressure was a great preventative in stopping any contamination from entering the supply line: it could still happen, but it is much more difficult.  Now with virtually zero pressure in the line, all forms of contaminants, sand, silt, dirt etc. are pretty much free to enter the water pipes through the multiple of places from where the water used to escape from.

The problem is further compounded by the fact that the pipes taking the returning sewerage back to the Water District for treatment, are often in parallel and fairly close to the potable water delivery lines.  You can be rest assured that these sewerage pipes will also have their fair share of leaks.

Now there is the possibility, if not probability, that some nasty little bacteria can find their way into the water supply lines.  These are usually around 1 to 3 microns in size and, along with other small suspended solids and all of the dissolved solids in the water, they will not be stopped by filters like the one seen in the picture. They are so small that you will not be able to see them with the naked eye whose resolving power (the smallest thing you can see) is around 40 microns, or 0.001575 of an inch or 0.004 of a centimeter..

Chris Salter is the President and Technical Director of H2O Profesionales Internacionales, S.A. de C.V. (www.aguadebaja.com), a water treatment company based in La Paz, who supply and install affordable whole-house water treatment systems.

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