A question that’s frequently asked is “How often should we test our water?” The answer depends somewhat on the source of the water for your dairy cows. The quick answer is to sample and analyze your water supply four times in a year. Pick the times of the year that are most likely to influence the water table: spring snow melt or rainy season, driest part of the year, and then points in between. This should give you a good baseline of the seasonal variation.
If your water comes from a shallow source, an unconsolidated (gravelly) aquifer, a very porous limestone, etc. it will be much more variable throughout the year and influenced by large weather events. A couple of years of 4x testing should give you a good sense of how much it varies, and which minerals are most influenced. If you want to know more about the underlying geology for your water supply, visit the US Geologic Survey Groundwater Information System. There, you can find maps, data and more about groundwater levels, quality, flow, etc.
If your water comes from a deep well, or is based in metamorphic or igneous bedrock, it will generally be more stable, but also more highly mineralized since that water has spent more time underground. Complete one year of 4x testing and if the results are pretty consistent, you can get away with sampling every couple of years.
Analyzing water quality is a minor investment in comparison to the benefits of understanding how much mineral your dairy cows are consuming from that source. When you get the analysis results back, run them through the evaluator at www.waterforcows.com so that you know if there are any complications from your water supply.