Integrating Rainwater and Groundwater for Domestic Water Supply in Ca Mau
A study co-authored by Dung Duc Tran (HAPRI Senior Research Associate) finds that using rainwater entirely for household water in Ca Mau Province would require large storage tanks, making that option difficult to achieve in the near future. In its place, the study introduces an integrated approach to storing rain and groundwater that the authors report has demonstrated high effectiveness and sustainability.
Context
Groundwater sources have been exploited excessively for numerous purposes worldwide, leading to increasingly severe depletion, yet replenishing them has not usually been a focus in economically and socially underdeveloped countries and regions. In the coastal provinces of the Vietnamese Mekong Delta, rural areas face difficulties in accessing fresh water because of shortages from the water supply plant and excessive use of groundwater.
Ca Mau is the southernmost coastal province of the Vietnamese Mekong Delta, where access to surface water sources during the dry season is challenging. In the province, groundwater is the primary water source for domestic needs, and it is facing severe depletion, evidenced by land subsidence of 0.5 to 4 cm annually, declining water levels and aquifer contamination. According to the paper, rainwater harvesting is currently limited across the province and does not fully utilize the available potential.
Methods
The authors interviewed 200 households in Ca Mau Province about the current situation of rainwater harvesting and the challenges and obstacles it faces. The survey was conducted in April 2020. They then analysed daily rainfall data from 10 meteorological stations, covering 1989 to 2017, to construct four scenarios with the water balance method: potential rainwater harvesting based on existing roof area; the optimal scale of storage tank and catchments for different levels of water usage; a tank scale that uses rainwater entirely during the rainy season and for basic needs during the dry season; and an integrated water supply combining rain and groundwater.
Key findings
Using rainwater entirely for domestic water supply requires large storage tank capacities, which the authors find makes these scenarios difficult to achieve in the near future.
Under the integrated approach with existing tank capacities of 0.8 m3 per person, rainwater could meet over 48% (14 m3 per year) of the water demand, while 14.8 m3 of additional groundwater extraction would be required.
With a tank capacity of 2.4 m3 per person, harvested rainwater could satisfy 64% of the demand, artificial groundwater supplementation would exceed 1.79 times the required extraction, and excess rainwater discharged into the environment would be minimal.
In the household survey, up to 84% of households said they do not want to increase their rainwater storage capacity.
Policy implications
The authors advocate for integrating rainwater and groundwater systems to enhance water resource management and self-sufficiency. The authors state that this approach can also be applied in urban areas, but that it needs strong support from local authorities via long-term official programs.
Keywords:
Rainwater Harvesting
Groundwater
Ca Mau Province
Vietnamese Mekong Delta
Water Management
Water Balance
Link:
Citation:
Vinh, D. H., Tran, D. D., Cham, D. D., Hang, P. T. T., Man, D. B., Mon, D., Tung, L. H., Kiem, L. V., Nguyen, T. D., & Tuyen, D. T. N. (2024). Integrated Exploitation of Rainwater and Groundwater: A Strategy for Water Self-Sufficiency in Ca Mau Province of the Mekong Delta. Hydrology, 11(4), 55.
