This question was posed by an ALN reader. We asked Vicki Lanphier at Edstrom to offer information on selecting an automated watering system.
The most important criteria to consider when selecting an automated watering system is how capable it will be at delivering quality drinking water that is free of variables that could otherwise compromise the research outcomes of the investigators. The Guide for the Care and Use of Laboratory Animals states, “animals should have access to potable, uncontaminated drinking water according to their particular requirements.” If control isn’t exerted over the water quality that the animals ingest, the potential for variability is introduced. An investment in an automated watering system should begin with an understanding of how such control is possible.
We should take a moment to distinguish between the various areas of an automated watering system. These areas include water delivery, purification, and treatment.
No matter what design is chosen, the water distribution lines need to be well thought out, with no dead legs or lines where water can stagnate. The piping needs to be constructed of materials that do not leach chemicals into the water and are resilient to chemicals the piping may come in contact with when delivering water, sanitizing the system, or treating the water.
There are two primary system designs for automated watering: flushing and recirculating. Flushing systems draw animal drinking water from a storage tank filled with purified water that contains residual disinfectant like chlorine. The pressurized system utilizes a computer program to control electronic solenoid valves that flush water through the system periodically. The flushing action provides a complete exchange of water and brings chlorine into all distribution piping and manifolds, ensuring that there is residual disinfectant available to kill any bacteria. Flushing can occur at either the room header pipe or through each individual rack. The online rack flush provides an added solution to assure that the watering manifolds remain clean. The flushing system flushes water to drain once a day or every other day.
The best recirculating system design is where treated water is pumped from the storage tank through distribution piping circuits all the way through the rack manifolds, which are connected to the return line that feeds back to the storage tank and passes through a UV light. This design provides distinct engineering challenges. Since water is constantly flowing through a number of different piping lines, flow control and pressure balancing are difficult to achieve. It is critical to have identical flow through every circuit and every manifold on the system.
A point to note, some recirculating system designs only flow water through the header piping and don’t flow water through the rack. This presents a problem since there is little water turnover in the manifold and could result in a high bacteria counts which could impact the research.
Here is a brief comparison of the two system designs. A recirculating system uses less water because there is no flushing occurring, but uses more energy because the pumps are running continually. The proper design of a recirculating system is more challenging to balance to ensure proper water turnover throughout all of the water distribution piping. A flushing system on the other hand does utilize more water, but very little energy and is an easier system to maintain over a long period of time.
The incoming water supplied by the local municipality to the facility should be assumed to be unsuitable for research animal consumption. Though the actual quality of the water may vary from place to place and season to season, the only way to fully understand what challenges municipal water presents is by preforming a comprehensive water quality test from the onset. This diagnostic should provide empirical data that includes the following: general bacteria and chemistry, radiochemistry, heavy metals, organic carbon and other organics, and the presence of herbicides. Once the incoming water quality has been analyzed and the results are known, a strategy can be put in place regarding how to achieve quality drinking water that meets facility requirements.
First, water purification is conducted to neutralize any native contaminates delivered with the incoming water supply. The methods of water purification are mechanical, and serve as a barrier that prevents foreign matter from passing downstream. Subsequent water treatment is then employed to prohibit new contaminants from developing. Water treatment introduces a residual disinfectant to the purified water that inhibits the growth of new contaminants over time.
In the most general sense, water purification can be understood as a series of filters that are adapted to catch smaller and smaller particles. Suspended particles down to 0.2 micron (μ) in size can be captured by cartridge filtration, which strains matter from the water. Filtration requiring capture of undissolved particles down to 0.02μ can be accomplished by ultrafiltration.
Reverse osmosis represents the ultimate barrier for impurities in drinking water. It can be used to seize particles all the way down to 0.001μ, achieving capture at the sub-molecular level. This process is so efficient that it is a method of choice for studies where specialized animal models are required, such as specific-pathogen-free and immune-compromised animals.
Water treatment involves the infusion of a measured amount of an acid or chlorine based disinfectant to the distribution piping of an automated watering system. The process of adding acid to drinking water, or acidification, has long been known as effective in prohibiting bacterial growth in water bottles used for animal consumption. That treatment is likewise effective with the automated delivery of animal drinking water. As a rule, the pH level of acidified water should fall between 2.6 and 3.0. Acidifying below 2.6 pH can cause decay of distribution system piping and should be avoided.
Chlorine, like acid treatment, is proven to be effective against renewed growth of bacteria in automated water systems. Chlorine concentrations as low as 2 parts per million (ppm) are effective at preventing bacterial colonization. However, unlike acid, chlorine concentrations dissipate with time. Additional volumes of chlorine can be reintroduced into the distribution piping by mechanical chlorine injection, or by introducing fresh volumes of chlorine during system flushing.
Make a Quality Decision
The level of water quality presented to research animals can be made as free of variability as required by the facility. From the accurate analysis of water quality testing, decisions can be made to build an automated water system that meets and maintains the needs of the investigators, and the animals that provide the gateway to the answers they seek.