Distribution process of the water supply in Iloilo
Metro Iloilo Water District covers the city of Iloilo and the towns of Oton, Pavia, Santa Barbara, Cabatuan, Maasin, and San Miguel.
At the sedimentation basin, natural sedimentation takes place. Raw water is fed with about one part per million of chlorine for sterilization.
The sedimentation facility consists of two basins, each having a size of 36 meters x 36 meters x 3.5 meters and with a capacity of 7,570 cubic meters. The basins, which work as one unit, are divided by a baffle wall in the middle, which purposely serves for the immediate settling of sand and slits.
The municipalities of Maasin and Cabatuan get their supply through water pipes branched from the conveyance pipeline.
The open reinforced concrete ground reservoir consists of two basins, each with a size of 48 meters x 74 meters x 6 meters and capacity of 41, 600 cubic meters. A concrete wall divides the two basins with several outlet valves connected to the distribution pipes installed along the wall. The wall serves to provide water during the cleaning of the basins. At this point, water from the open reservoir undergoes several stages of purification at the water treatment plant. The plant has the capacity of 37,000 cubic meters per day. Treatment of raw water involves the following stages: rapid mixing coagulation/flocculation, filtration and chlorination.
From the water treatment plant, water is then delivered by gravity to Iloilo City passing through a 7, 500/ cubic meter covered reservoir located several meters away from the open reservoir through the main pipelines measuring 28, 26, 24, 22, 20,and 18 inches in diameter with the 24 -inch parallel lines interconnected with each other.
Supply for Iloilo City, including its nearby districts, supplemented by the eight (8) production wells from San Miguel and Oton with a combined capacity of 13.800 cubic meters per day. Another production well in Santa Monica, Oton with a capacity of 2, 160 cubic maters per day supplies the water requirement solely of the municipality.
The Purification ProcessesTreatment of raw water, first and foremost, undergoes rapid mixing. During this stage, raw water from the pumping structure passes through the flash mixer wherein chemicals like chlorine (for pre-chlorination) and aluminum sulfate are applied to remove the turbidity of water. From the flash mixer, water flows to the pulsator where coagulation/flocculation occurs. Coagulation is the process of changing from the fluid to a thickened mass. Flocculation, on the other hand, is the massing together of discharged particles, which are brought into contact with one another by mixing that, will eventually lead to the formation of flocs. Sedimentation also takes place whereby heavy matters are allowed to settle at the bottom. What follows after this is filtration at the aquazur filters whereby water is filtered though a series of their beds consisting of several layers of graded sand. Although water can already be considered pure after filtration, still MIWD does not take any chances. The water, even if pre treated with chemicals, has still to be treated again with a disinfectant to get rid of bacteria. Chlorination is the final stage in the purification process. The application of chlorine depends on the turbidity of raw water, provided, the residual chlorine is maintained at least one milligram per liter. As soon as this is done, water is now ready for the distribution system. |
Water quality monitoring
MIWD regularly conducts bacteriological testing of all its ground and surface water sources. From hundred of sampling points located representatively in the distribution system, at least three samples are taken from those points every week. The minimum number of water samples collected monthly from the distribution system from consumer taps is based on the requirements of the Philippine National Standards for Drinking Water. i.e. for a level three supply system, the minimum requirements should be 20 samples plus 1 sample per 10,000 population. MIWD, however exceeds this number of samples by 500-800% monthly.
The MIWD system of water sampling and testing enables it to get a good picture of the bacteriological quality of water supplied and distributed to the service area. One hundred percent of the total number of water samples taken from the distribution system is located from fixed sampling points every month.
The location points is such that the water samples tested are representative of the water supplied to the distribution system and enables proper supervision and control of this bacteriological qualities of water.
Aside from the regular sampling points, special samples are collected, focusing on bacteriologically unsatisfactory points to ensure detection and localization of water contamination and are concentrated over a smaller cluster of locality. These samples are not part of the regular sampling frequency and are not used as a basis for evaluation of the bacteriological quality of water supply.
1.) CLUSTER SAMPLES
After a point of any part of the system indicates bacteriologically unsatisfactory water quality, minimums of three cluster samples are taken to determine the extent geographically. It required, additional cluster samples are collected and the area of concentration expanded until the contamination has been localized or contained. In instances of consumer-initiated complaints on water quality, which is presumptive of water contamination, to minimum of five cluster samples are taken.
2.) RES-SAMPLES
After determining the extent of contamination and taking corrective action to eliminate the source of pollution, two consecutive negative re samples are required before the point or area is cleared of contamination. Re- samples are also taken from cluster points.
Bacteriological tests
The bacteriological analysis of water is the most valuable examination and is vital in preventing epidemic brought by water pollution.
This involves the estimation of bacterial estimation of bacterial density determined from the most probable number and from the significant detection of the presence or absence of numbers of the coliform group of bacteria. The coliform group includes all aerobic, facultative, anaerobic gram negative non-spore forming bacilli, which ferment lactose broth with gas formation. Formation of gas in the lactose broth media within 24 hours is the presumptive evidence of the presence of the number of group.
Further confirmatory and completed tests are then carried out to confirm the presence of these coliforms.
Standards for Drinking Water
MIWD follows the limits established by the National Standards for Drinking Water and by the U.S Public Health Service Drinking Water Standards. The bacteriological quality of water in the distribution system is monitored according to the following standards:
a.) When 10 ml standard portions of a single sample are examined per month in the multiple tube fermentation method, not more than 5% of all water samples examined shall indicate the presence of the coliform group bacteria.
b.) The presence of thermotolerant and fecal coliforms must not be defected in any 10 ml standard portions of a water sample.
The above is deemed the minimum requirements for bacteriological quality of drinking water supply. The Metro Iloilo Water District maintains the quality of its water supply in conditions better than these minimum standards. Aside from the bacteriological water quality parameters, monitoring and evaluation of the physical and chemical quality of the water supply is also conducted. The Metro Iloilo Water District regularly tests its ground water and surface water sources or its physical parameters and the presence or concentration of chemicals substances that may affect potability and endanger health.