Share thisWater quality, cost of water, and system operations are some of the factors in determining the method to deliver water and to keep it bacteria-free.
Maintaining cage racks is a time consuming and labor-intensive activity that can place an enormous burden on laboratory technicians that work in animal facilities. This task is also not the most pleasant one as it involves replacing soiled bedding as well as changing out water bottles. However, improvements in rack ventilation have allowed the frequency of cage cleaning to drop off dramatically by helping to keep bedding dry and by reducing odors. Because water bottles are normally changed when the cage is cleaned, the laborsaving benefits of these extended cleaning cycles cannot be fully realized unless an automated watering system is employed. Anyone who has had the responsibility for cleaning cages or who has had to hire and maintain a staff of technicians to do this work understands the value that both ventilated cage racks and automated watering systems can provide. When it comes to automatic watering systems, there are a couple of methods to choose from with each having advantages depending on the particular application.
Re-circulating
Re-circulation systems require a water treatment system to keep the water clean since “fresh” water is introduced into the system only as fast as it is consumed by the animals, which is usually at a very low rate. The treatment system involves pre-filtration to remove gross particles that can compromise the function of the watering system and a water purification system such as reverse osmosis. Of all the contaminants in the water supply, bacteria is the hardest to control and can live in purified water which contains very few nutrients. The bacteria can go into a low nutrient mode where they reduce in size and bond to the internal surfaces of watering systems. Bacteria will attach to any surface that water contacts and develop what is termed a biofilm. Biofilm development will occur in animal watering system piping and, as the biofilm grows, pieces of it can detach and flow downstream to be consumed by the animals. Reverse osmosis (RO) is a water purification process in which water is forced by pressure through a semi-permeable membrane. In normal osmosis, water flows from a less concentrated solution through a semi-permeable membrane to a more concentrated solution. Reverse osmosis uses pressure to reverse normal osmotic flow. Water flows from a more concentrated solution through a semi-permeable membrane to a less concentrated solution. The feedwa-ter to the reverse osmosis system flows over the surface of the membrane and a percentage of the water is forced through by pressure and becomes the purified water or permeate. The remaining water, concentrate, retains the rejected contaminants and is drained off. The percentage of feedwater that is recovered as permeate, called percent recovery, is typically 33 or 50 percent. The other 66 or 50 percent is discharged to drain.
Flow in a re-circulating system occurs in a loop, meaning that the water travels in a continuous circle throughout the animal facility without any branching off. Water flows from a storage tank, through an ultraviolet disinfection unit, to the room distribution system, with unused, purified water returning to the storage tank. This loop design requires flow rates between three and six feet per second, which is a very important design consideration. These minimum velocities help to prevent the bacterial adhesion that can lead to the formation of biofilm. The loop flow rate will vary, being higher at the beginning and gradually decreasing towards the end as flow branches off and is consumed at each cage station. To keep velocities up, the diameter of the pipe can be decreased along the length of the loop. Installing a flow meter at the end of the loop will allow for verification that minimum velocities are maintained.