Santa Rosa River
The City is principally drained by the Santa Rosa River, Diezmo River and Cabuyao River which all flow from the mountainous area of Silang, Cavite towards Laguna de Bay. Water flowing at the Santa Rosa River comes from the watersheds of neighboring Cavite.
The river acts as a natural boundary from the Municipality of Biñan before it drains into Laguna de Bay. The DENR categorizes the river as class C, meaning it is only suitable for aquaculture, fisheries, recreation and extraction for industrial uses. Serving as natural boundaries between Santa Rosa and Cabuyao are the Diezmo River and Cabuyao River.
Easements of 3-4 meters from both sides throughout the entire length of any river are considered environmentally critical and are subject to easement for public use for recreation, fishing, among others.
Santa Rosa is located in the western part of Laguna de Bay,the largest lake in the Philippines, also referred to as Laguna Lake. The lake has a total surface area of 90,000 hectares, an average depth of 2.8 meters, and a total volume of 3.2 billion cubic meters. There are 21 tributaries contributing to the lake and among these are the rivers of Santa Rosa.
The lake water is only suitable for aquaculture, fisheries, recreational activities and industrial uses. Although the lake is naturally euphoric and highly productive, it is polluted as a result of human activities in the watershed carried via tributaries or directly into the lake. For example, the discharged raw sewage into waterways is transported to the lake thus contributing to excessive ammonia, a cause of fish kills.
Residents living in the lakeside areas of Santa Rosa rely on fishing for sustenance and profit base or concrete pedestal; (5) well located on top of canal or waterway; (6) poor condition of casing, pump assembly/parts; and (7) proximity to and location down gradient of toilet or septic tank. These conditions are aggravated by flooding and the regular use of the well area for washing and bathing, which facilitated entry of contaminated water into the aquifer through the well casings or openings on the ground.
Among the 18 barangays, the wells used for drinking in the lakeshore barangays of Sinalhan, Aplaya and Caingin would be most vulnerable to water contamination due to floods in these areas.
Surface Water Quality
Neither the DENR nor the LLDA monitors Santa Rosa River’s water quality. However, an Environmental Impact Study conducted for the proposal of the Santa Rosa Business Park undertook a water quality study. The study concluded that the Santa Rosa river exhibited very good upstream quality but poor downstream quality.
The lake, however, has undergone extensive and continuing study because of its role as the most significant resource in the area. In 1996, the LLDA conducted a water quality study which monitored several points in the lake and within selected tributary rivers. The station in closest proximity to Santa Rosa was Station 1 or the West Bay located south of the mouth of Pasig River and northeast of the municipality. The study did not include sampling within the municipality itself.
However, since the only outlet for the bay is the Pasig River, it is conceivable that any negative impacts of Santa Rosa to the Lake can somewhat be implied by quality monitored at this point. Temperature stayed within allowable limits as did pH, dissolved oxygen, biological oxygen demand, chemical oxygen demand, nitrate, ammonia, total dissolved solids, total suspended solids, chloride, oil and grease, chromium, and copper.
Due to the good water bearing capabilities of the alluvium and clastic rocks underlain in Santa Rosa, groundwater resources are accessible. Most of the areas in the City, except the lakeshore barangays, Pulong Sta. Cruz, Malitlit, Don Jose and Sto. Domingo, can utilize potentially high yielding wells .. Areas in Pulong Sta. Cruz, Malitlit Don Jose and Sto. Domingo need to dig deeper wells to access groundwater.
However, saltwater intrusion can happen when waters from Manila Bay flush into the lake and lakeshore communities exceed the safe yield limits of their aquifers.
In 2009 the local government of Sta. Rosa, in cooperation with Coca Cola Foundation and World Wildlife Fund for Nature (WWF)-Philippines conducted a wellhead assessment project to assess the condition of well heads and the immediate vicinity of public wells which are used for drinking, and to recommend mitigation measures to reduce health risks and contamination of the aquifer system. This project was a preliminary effort to ensure the sustainability of the groundwater resource in Sta. Rosa City.
The full inventory of wells has identified a total of 1,866 communal wells in 18 barangays. Among these wells, about 1,104 have been used for drinking purposes by around 8,465 families. Majority of these wells are located in barangays Aplaya, Caingin and Sinalhan. The shallowest wells are also located in these lakeshore barangays, indicating the proximity of groundwater to the surface water areas. About 80 of the wells were established during the last 20 years, while 20 of the wells have been used for more than 20 years. Seventy-seven (77) wells were selected for sampling and potability test for total coliform. Out of the 77 wells, 26 wells tested positive for total coliform and from these number about 12 wells were found to be positive to fecal coliform (Escherichia coli or E. coIl). The study identified possible sources of total and fecal coliform in groundwater such as agricultural runoff, effluent from septic tank systems or sewage discharges and infiltration of domestic or animal fecal matter. Fecal coliform in deepwell water suggests recent groundwater contamination (or the aquifer system) from sewage or from animal waste.
The study has also identified seven (7) possible cases of unfavorable physical conditions within the immediate well area which have contributed to the contamination of aquifer, and these include (1) submerged well base; (2) well near canal and waterways; (3) cracked well concrete base; (4) absence of a concrete