James:
I’ve considered as an emergency water supply the steady runoff from the cornfield behind us. It’s always at least a steady trickle even in the driest part of summer. Will a Katadyn filter or similar remove pesticides or other chemicals from it? Or should I plan on a small water still? – Mike
JWR Replies: If working with field runoff, first use a pre-filter to remove sediment. Just a couple of thicknesses of T-shirts over a five gallon bucket works fine as a pre-filter. Using pre-filtered water will greatly extend the life of your primary filter. Next, to filter out the majority of herbicides and pesticides, you should use a two-stage filter such as a Katadyn Combi Plus filter. These are available from a variety of Internet mail order vendors, such as Dom’s Outfitters [1]. However, keep in mind that if runoff water ever become the your main supply of water in an extended disaster situation, no filter system is 100% effective at removing herbicides and pesticides. For that, you would need either a distillation or reverse osmosis system, which are far more complex and have large power requirements.