Bare Facts

Putting science to the water crisis – 9

By Engr. Edgar Mana-ay

IN MY May 14 article, this writer suggested that the city, on its own, take a direct hand in putting up of a series of mini bulk water processing plants at the barangay level to help alleviate the perennial water shortage.

This is really an interim solution until our water utility, Metro Iloilo Water District (MIWD), can effectively and totally solve the water shortage for the entire Iloilo City, which may take another 10 to 20 years, a very optimistic forecast.

A district or barangay level water supply system is NOT an ideal public water supply system, although this is widely used in Cebu City and other cities in the country, as far as water cost and quality is concerned.

This is also not applicable in all areas of the city if there is NO suitable LOCAL water source, compared to the coverage of a water utility like MIWD or Balibago Waters whose source is a large river from a large watershed.

BUT with the present state of the water situation, a desperate method for a desperate situation will have to be made to alleviate the sufferings of the people in the most affected areas such as Veterans Village and many other barangays of the City who are never recipients of potable water from MIWD.

To implement this water project, the foremost task is to define a local water source, which, in 90 percent of the intended beneficary areas, will come from the underground water resource. A cluster of homes will then be determined to match the available water resource.

Further, the premise is that this mini water plant will access underground water up to 80 to 100 ft. deep only and that its saltiness will not exceed 900 tds (total dissolve solids) because Department of Health (DOH) TDS standard for drinking water is 500. Beyond the 1,000 TDS in underground water source, reverse osmosis (RO) process will have to be used which is avery expensive way to produce potable water for a barangay.

A hydro-geological assessment of the priority barangays will have to be made in implementing this project. The small scale water projects envision to supply 5,000 gallons or 19,000 liters per day, operating at 8 hours per day, to serve the potable water needs of 1,000 residents (at 20 liters per person per day).

Therefore, we will have to forego with many of the standard but expensive hydrogeology investigations like resistivity surveys. Instead, actual experience and the hit-and-miss method of looking for water underground will be used. As the manual drilling proceeds, the cuttings or the ground portion being bailed out to the surface is “read” for every two feet drill penetration to determine if such ground strata is water bearing.

An expert “reader” is certainly better than all the scientific equipment such as electric logging to determine water bearing horizon or “aquifer” underground because of the visual and human feel.

The cutoff of a maximum 100 ft. source of underground water is used because that is the limit of depth that a common, inexpensive surface centrifugal electric pump can be used whose cost will not exceed P30,000 at maximum 7-1/2 horsepower.

Besides well drilling, using the local well contractors with antiquated manual percussion method is still very effective and inexpensive up to that depth. However beyond 100 ft. deep, well cost will be tripled because it will require a machine driven drill and the use of a submersible pump whose cost is more than P100,000 for the same 7-1/2-horsepower surface centrifugal pump.

Once a 60 to 80 ft. well is completely drilled and the cuttings read so that initial conclusion is made that it is a potential 10 to 12 gal./minute, a manual pump test will be conducted using a pitcher pump to manually confirm tge well yield.

A representative sample of the water then be taken for TDS and bacteria analysis. For as long as the volume (minimum of 12 gal/min) and TDS (maximum of 900) cutoffs are attained, then the well is a go. Meaning, a 3-inch casing can now be installed with perforations in line with the identified aquifer or waterbearing horizon. Then all the other well appurtenances such as electric pump, electrical and pipelines connections and a 200-gallon stainless water storage tank are installed.

The most important part of the water system is the filter system. This is a multi-media filter system enclosed in steel about the shape and size of a 55 gal.drum. Inside is a combination of filtrate in the form of coarse sand, corn size pebbles, and pulverized coal that is very effective in filtering dirt, mud and iron, and manganese pollution that cause reddish stains on our laundry.

A backwash system will clean the filter elements as often as you want it cleaned, so that in theory this is a forever filter system with nothing to replace; unlike the commercial filters where one has to buy a replacement element periodically.

If the City government adopts this barangay level mini water supply system, then it should provide a budget of P500,000 per plant to alleviate the water woes of 1,000 residents.

Since this is a very simple system to operate, the recipients of the water should run it themselves with the guidance of the Barangay officials. This is a temporary measure until MIWD can fully supply your water maybe in 10 to 20 years from now.

Note: The author is a Professional Member of the Water Treatment Industry Group of the U.S. (WTIG).