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. 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.