In 1999 the U.K. Government amended the Water Supply Regulation applying to England and Wales. From March 2000 all Water Treatment Plants at risk of releasing Cryptosporidium into drinking water supplies must monitor continuously for Cryptosporidium.

Prior to the new regulations being introduced, the Government's Drinking Water Inspectorate (DWI) carried out studies into the feasibility of sampling 1000 litre of treated water per day, and of detecting 100 Cryptosporidium oocysts in the sample.

Hydraulics Modelling Services were asked to produce a prototype Cryptosporidium Monitoring Unit (CMU). The purpose of the unit was to house a filter module which would retain the Cryptosporidium oocysts for laboratory analysis, and to measure all the relevant parameters e.g. module inlet and outlet pressures, flow throughput, flow rate etc. Many alarms linked to telemetry lineswere also required to enable the quick response to filter blockage or equipment failure. The oocysts are filtered and retained in a filter module housed in the CMU. The module is taken to a laboratory for analysis.

Over a period of a year the design of the unit evolved through the construction of 6 prototypes. Each one went through site trials at treatment plants around England. Eventually a final design was arrived at which then formed the basis for a specification to be included in the new regulations.

Following the introduction of the regulations HMS has built over 200 CMU's and supplied all the major Water Companies of England and Wales