displacement pump is proportional to the flow rate of the supplied water as this flow rate changes the operating speed of the pump changes and thus the quantity of additives injected into the stream also changes this results in an additive concentration in the water which is relatively constant over a wide range of flow rates as shown in fig1 all of the inlet hoses 14 connect to a single additive source in this regard and as shown in fig2 each of the inlets 50 may be removed to reduce or eliminate the flow of additive from the external source into that inlet 50 this arrangement would allow in a situation where all the inlets connect to a single additive source the concentration of the additive in the outgoing stream of intermixed water and additives to be varied by enabling or disabling the flow of additives through a particular inlet this type of concentration control is possible since the positive displacement pump sequentially injects a quantum of additive from each inlet 50 into the water stream consequently disconnecting any one inlet 50 will result in the corresponding quantum of additive not being taken and the concentration of the additive in the resulting mixture will thereby change additionally each of the inlets 50 may be connected to a different type of additive for example one inlet could go to artificial coloring one to insecticide one to herbicide and one.