when you get rain don't use the water from the tanks. lay the fabric out on the grass or outdoor furniture and let it rain on it. then let it dry outdoors. that might freshen it up. be patient. you may have to do it more than once, but it sounds like it will be worth it.
or, can you take it to a nearby river or beach? water is water. this would only be a stop-gap measure. later on, you can wash it properly one piece at a time when you can afford to spend your own water.