Water security is fundamental to human security. Initially viewed as a water scarcity issue, water security is now looked at holistically, encompassing several dimensions. In the last few years, there have been rapid strides made in water security research. This has led to an improved and a more all-inclusive understanding of water security and has, to some extent, unravelled the inherent complexities that are associated with it. While science has been quite successful in explaining the theoretical aspects of water security, there is much scope to link these to real world solutions. The philosophy of water security is robust; however, its implementation on the ground is still weak. Research in water security now needs to move into this solution space, where the theories are translated into practice. This paper provides an overview of the existing water security landscape, and seeks to identify some key research needs that are required to operationalize the concept of water security into reality. It acknowledges that achieving water security may be a complex process, requiring the coordinated and concerted efforts from several stakeholders and diverse water use sectors. However, the creation of water-secure societies with an acceptable level of risk is very much possible. Science has a large role to play in making this happen.

　The Talbot formula R = at /(t + b) and the Sherman formula R = ctⁿ were fitted to the relation between probable rainfall depth and duration, where R and t respectively represent the probable rainfall depth and the duration, and a, b, c, and n are constants.

　On the whole, value n in the Sherman equation and value b in the Talbot equation, both of which represent the continuity of heavy rainfall, respectively decreases and increases as the durations in a duration range increase. However, the variations of the values with the duration range are markedly different among stations.

　When the magnitude of the variation of a constant in a rainfall depth-duration formula with the duration range is expressed by the coefficient of variation, a strong negative correlation can be found between the coefficients of variation of the constants in the Talbot and the Sherman formulas.

　For durations in a duration range that are short (e.g., 1-24 h) or long (e.g., 10-72 h), the number of stations at which the Sherman formula provides the better fit is greater. For durations in a duration range that are medium (e.g., 3-40 h), the number of stations at which the Talbot formula provides the better fit is greater. The constants in a rainfall depth-duration formula that provides the better fit vary little with the duration range. In southern and northern Japan, respectively, the Sherman and the Talbot formulas provide the better fit.

　Lake Teganuma had the worst COD quality of any lake in Japan. To improve water quality, a water-conveyance facility from the Tone River (9 m³/s maximum discharge) was introduced by the North Chiba pipeline project in 2000. The project, the first large-scale lake water-conveyance pipeline project in Japan, has decreased COD concentrations in Lake Teganuma dramatically. In fact, the COD loads of Lake Teganuma were reduced by about 10 %. The project also improved the Tone River water quality because Lake Teganuma flows into the Tone River. Data analysis has revealed that the COD concentrations in Lake Teganuma vary according to rainfall and pump discharge by the water-conveyance facility. For effective water supply management, the authors demonstrated the possibility of further reducing Lake Teganuma COD concentrations by changing the pump discharge once a week for 6 months according to the daily average COD concentration and weather conditions.