I got the 55 gallon blue plastic drums for $10 each from the local Pepsi bottling company. Get a couple and that takes care of the water for one horse for 11 days. Can't remember where I ordered the plastic pump but it wasn't spendy.

Oops, I had a morning brain cramp when I wrote this - opening the fairgrounds would definitely not work in Lewis County, as Susan points out the fairgrounds are thoroughly under water in most any flood. What I meant to say at 8.30AM without benefit of coffee was that the pre-planning among local land owners and live stock holders on safe pasturage sites works in Lewis and King County. But only the King County fairgrounds in Enumclaw is above the high water mark - it may be in the flow of a lahar off of Mt Rainier, but if the lahar is your disaster I submit horses and owners have far more important problems than potable water.

Also it may be that Island County EM does have a plan to cart water to horses and not to cart horses to water, but Island County is made up of smallish islands with some unique capabilities and needs: they may have a water carrying vehicle stationed on islands with significant animal populations and a plan to water them. That's fine on smallish islands, but it generally doesn't scale if you were talking county-wide animal watering in most counties (including King).

In my county here in SoCal, it is fairly common to move horses and other large animals out of the path of wildfires, almost always to the county fairgrounds. Alternative locations are available as well.

A handy temporary water container that stores 'small' when not in use would be this:

http://www.amazon.com/Toro-29210-43-Gallon-Gardening-Spring/dp/B000E7SU3I/ref=pd_bxgy_ol_text_c

Lined with a heavy duty contractor 55 gal trash bag it would work as a temp horse watering trough (under supervision...).

I don't know how well a couple of these would work in the back of a pickup for transport unless you restricted their movement. Obviously you would need to tie the bag of water closed inside the container, too.

You would need to experiment before an actual serious 'need' arose.

The-what I would call a leaf container-could be used for gardening/yard duties in the interim.

Just an idea.....
gimpy

if there is a tiny stream above your property, even as far as a 1/4 mile off, where you can shallow-bury a 1/2" poly-pipe to a stock tank, you can have water year-round.

we only had to go a few hundred yards to get gravity-fed water for the horses. water movement keeps it from freezing even when below zero.

Now that's a clever idea!

Do you screen the intake end or anything?

Sue

yep sue, just used a hose-clamp and some old window-screen mesh (fiberglass or metal). needs to be cleaned/checked twice a year.