External auxiliary potable water tank recommendations?

Thanks for these ideas. I found a 1000L tank online similar to some I have seen in use by other seasonal campers here since my original post. Wish I knew how to embed a pic in this post. I plan to live full time in the trailer next summer and want to have plenty on hand for use inside and with an outdoor shower I hope to rig up.

Good points mentioned though... pump, cover, algae concerns. Thanks.