PUMP CONTROL SYSTEM FIELD OF THE INVENTION The invention relates to a pump control system that 5 minimizes consumed energy by operating a plurality of pumps at an optimal efficiency point in a control system that operates the plurality of pumps arranged in parallel for water distribution of a water supply. Further, the invention relates to a pump control system that can maintain an operation at the 10 optimal efficiency point even in the case where a pump characteristic deteriorates as time elapsed. BACKGROUND OF THE INVENTION Japanese Unexamined Patent Application Publication No. 15 2005-76452 discloses a method for actualizing energy saving operation of a plurality of pumps by acquiring a maximum efficiency curve that maximum efficiency points in rotating speeds of pumps are plotted, setting a number change flow curve for an increased number of pumps and a number change flow curve 20 for a reduced number of pumps parallel thereto, and changing the operating number of the pumps to be increased or reduced when a discharge flow rate exceeds the change flow curves due to a property of a discharge quantity Q-a discharge pressure H, in order to appropriately judge the operating number of a 25 plurality of variable-speed pumps. .. 3 Japanese Unexamined Patent Application Publication No. 2010-216288 discloses a parallel-off control method of parallel pumps by calling a flow rate when the sum of axial drive force after parallel-off operation is equal to the sum of axial drive 5 force before the parallel-off as an energy saving parallel-off flow rate, calculating the energy saving parallel-off flow rate from a set multiplier, a lifting height-flow rate approximate expression, an efficiency approximate expression of the pump and the number of parallel pumps, the number of parallel pumps, 10 and a detection of an intake lifting height, setting this value, and determining the operating number of the pumps based thereon, in a parallel-off control system of the parallel pumps controlled by discharge pressure constant control or estimated end pressure constant control, which saves energy as compared 15 with the related art. SUMMARY OF THE INVENTION Japanese Unexamined Patent Application Publication No. 2005-76452 described above discloses the method of increasing 20 and reducing the operating number of the pumps in order to actualize the energy saving operation by considering the efficiency characteristic curve of the pump, but when a plurality of pumps having differen~ characteristics is used, even a distributed water flow rate which each pump takes charge 25 of needs to be determined as well in addition to the operating 4 number. In the related art, this point is not considered and there is a doubt about advanced energy saving operation. Further, since time-elapsed deterioration in the pump characteristic is not considered, the operation cannot be 5 performed at an efficiency point as time elapsed, and as a resul t, excessive power is consumed. Further, in Japanese Unexamined Patent Application Publication No. 2010-216288 described above, an optimal number change-over timing flow rate is determined by considering a 10 total axis drive force of the pump, but the application of the technology is limited to the discharge pressure constant control or the estimated end pressure constant control and the technology cannot be applied to more highly advanced control. In addition, since the number change-over flow rate 15 (parallel-off flow rate) is determined based on the total axis drive force which does not particularly coincide with total energy consumption of the pump, precise minimization of consumed energy cannot be actualized. Moreover, a number change-over operating state depends on a pressure as well as 20 the flow rate, but a number change-over timing (parallel-off timing) is determined by only the flow rate and precise change-over to actualize energy saving cannot be performed. Further, since the time-elapsed deterioration in the pump characteristic is not considered, the operation cannot be 25 performed at the efficiency point as time elapsed, and as a 5 result, the excessive power is consumed. The invention is contrived by considering the situations and an obj ect of the invention is to provide a pump control system that actualizes minimization of consumed energy by acquiring 5 both the operating number to actualize energy saving and an optimal distribution water flow rate which each pump takes charge of. Further, another object of the invention is to provide a pump control system that can maintain operation of the pump at an optimal efficiency point regardless of time by 10 estimating a characteristic curve of the pump on-line and using the estimated characteristic curve in efficient operation of the pump. A pump control system controlling operation of a plurality of pumps according to the first aspect of the 15 invention includes: a storage unit configured to store an operating number judging table determining the number of pumps to be operated in accordance with a distributed water flow rate and a discharge pressure and a flow rate distributing table determining distribution of the distributed water flow rate to 20 each pump in accordance with the number of pumps, the distributed water flow rate, and the discharge pressure; an operating number judging unit configured to refer to the operating number judging table and determine the number of pumps to be operated based on the distributed water flow rate and the 25 discharge pressure; a distributed water flow rate calculating 6 unit configured to calculate distribution of the distributed water flow rate to each pump based on the number of pumps to be operated, the distributed water flow rate determined by the flow rate distributing table, and the discharge pressure; and 5 a target rotating number calculating unit configured to set a target rotating number of each pump based on the number of pumps to be operated, which is stored in the operating number judging table and the distribution of the distributed water flow rate to each pump, which is acquired by the distributed water flow 10 rate calculating unit. In the pump control system according to the second aspect of the invention, in the case of the number of pumps determined by the operating number judging table and the distributed water flow rate determined by the flow rate distributing table, a 15 characteristic curve representing a characteristic of each pump, the operating number of pumps in which consumed energy of all of the respective pumps operated in accordance with a predetermined operating sequence is minimized, and the distributed water flow rate distributed to each pump are 20 acquired for each distributed water flow rate and discharge pressure. The pump control system according to the third aspect of the invention further includes a pump characteristic estimating unit configured to measure the distributed water flow rate of 25 the pump, the discharge pressure, the rotating number of each e 7 pump, and power consumption of each pump, and estimate the characteristic of each pump based on information from the measurement. In the pump control system according to the fourth aspect 5 of the invention, the pump characteristic estimating unit measures the distributed water flow rate, the discharge pressure, and the rotating number and the power consumption of each pump when each pump is operated by changing a parameter for determining a characteristic curve and a performance curve 10 representing the characteristic of each pump determined based on the distributed water flow rate and the discharge pressure of the pump, the rotating number of each pump, and the power consumption of each pump, which are measured, to a set value different from an original set value, and estimates the 15 characteristic of each pump based on information from the measurement. In the pump control system according to the fifth aspect of the invention, as the characteristic curve of the pump of the second aspect, the characteristic of the pump estimated of 20 the third aspect is used. In the pump control system according to the sixth aspect of the invention, as the characteristic curve of the pump in the second aspect, the characteristic of the pump estimated in the fourth aspect is used. 25 According to the invention, since the operating number 8 of the pumps and the flow rate distribution of the pump at which the total consumed energy of the pump is minimized are determined based on two variables of the distributed water flow rate and the discharge pressure that define the operation of 5 the pump, the energy of the pump control system can be saved. Since the characteristic of the pump is estimated from the measurement data, and the operating number of the pumps and the flow rate distribution of the pump are determined based on the recent estimation characteristic, the operation can be 10 maintained at the optimal efficiency point regardless of the temporal change of the pump characteristic. Further, the operation can be actualized in the wider operating area on-line by operating the pump with a parameter different from the original parameter. Accordingly, since the pump 15 characteristic can be estimated with high precision by using the measured data, the reliability of the operation at the optimal efficiency point can be improved and the increase in the power consumption can be maximally suppressed. 20 25 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of a pump control system of a first embodiment of the invention; FIG. 2 illustrates an operating number judging table of a pump; FIGS. 3A and 3B illustrate a flow rate distribution 9 calculating table of the pump; FIG. 4 is a processing flowchart for preparing table data; FIG. 5 illustrates one example of a database storing an optimal solution; 5 FIG. 6 is an explanatory diagram of calculation of consumed energy by operating the pump; FIG. 7 is a processing flowchart of a program to calculate a target rotating number of the pump; FIGS. 8A and 8B illustrate one example of a performance 10 curve and an efficiency curve of the pump, and time-elapsed deterioration; FIGS. 9A and 9B illustrate measurement data by actual operation; FIG. 10 is a configuration diagram of a pump control system 15 of a second embodiment of the invention; FIG. 11 illustrates one example of measurement data stored in a database; FIG. 12 is a configuration diagram of a pump control system of a third embodiment of the invention; 20 FIG. 13 is a configuration diagram of a pump control system of a fourth embodiment of the invention; FIG. 14 illustrates one example of a modified operating number judging table; FIG. 15 is a configuration diagram of a pump control system 25 of a fifth embodiment of the invention; and 5 10 FIGS. 16A and 16B illustrate one example of flow rate distribution correction calculation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the invention will be described with reference to the accompanying drawings. A first embodiment will be described with reference to FIGS. 1 to 7. FIG. 1 is a configuration diagram of a pump control system of the first embodiment. A control system includes a water 10 distributing pipe 1, a distribution reservoir 11, a pressure sensor 2 measuring a discharge pressure, a flow rate sensor 3 measuring a distributed water flow rate, variable-speed pumps 4, 5, and 6, rotating number sensors 7, 8, and 9 measuring a rotating number of a pump, a target discharge pressure, a 15 measured discharge pressure, a pump control system 100 calculating a target rotating number of each pump like actualization of the target discharge pressure by using the measured distributed water flow rate as an input, and PID control devices 12, 13, and 14 adjusting input signals in 20 respective pumps so that the measured rotating number coincides wi th the target rotating number. In FIG. 1, an example in which three pumps are arranged in parallel is illustrated, but the other number of pumps may be installed. The operating number of pumps is increased with an increase in the distributed water 25 flow rate. Herein, when the flow rate is small (little), only 20 11 the pump 4 is operated, the pumps 5 and 6 are added in sequence with the increase in the flow rate, and the operating number of pumps is increased. The distributed water flow rate measured by the flow rate 5 sensor 3 is changed momentarily according to a water demand. The pump control system 100 calculates the target rotating number (when the rotating number is 0, it is regarded that the pump stops) of each pump so that the discharge pressure measurement value by the pressure sensor 2 coincides with the 10 target discharge pressure wi th respect to the change in the flow rate. Combinations of rotating numbers to actualize the target discharge pressure are provided beyond number, but the pump control system calculates a rotating number combination that enables minimum consumed energy. In order to actualize the 15 combination, the pump control system includes an operating number judging unit 101, an operating number judging table 102, a flow rate distribution calculating unit 103, a flow rate distributing table 104, and a target rotating number calculating unit 105. Further, the aforementioned units of the pump control system are actually executed by software programs for actualizing respective functions thereof. The software programs are configured by, for example, modules including the respective units and the control unit such as a CPU, and the 25 like reads and executes the software programs or the 20 12 aforementioned respective tables from a recording device such as an HDD, and the like as actual hardware, and as a result, the respective units are loaded on a main storage device and the respective units such as the operating number judging unit 5 101, the flow rate distribution calculating unit 103, and the target rotating number calculating unit 105 are created on the main storage device. The operating number judging unit 101 determines the number of pumps to be operated by referring to the operating 10 number judging table 102 which is constructed in advance. An example of the operating number judging table 102 is illustrated in FIG. 2. A horizontal axis and a vertical axis represent a discharge pressure H and a distributed water flow rate Q, respectively. The small flow rate (when the flow rate is small) 15 is a 1-pump operating area (only the pump 4 is operated) , a medium flow rate (when the flow rate is medium) is a 2-pump operating area (two pumps of the pumps 4 and 5 are operated), and the large flow rate (when the flow rate is large) is a 3-pump operating area. As boundaries of the respective areas, two lines, a solid line and a dotted line, are provided. The solid line is a number change-over line used when the operating number