Water shortages do not have to trouble the world-if we we start valuing water more than we have in the past.
不懂这个have，为什么不需要过去式？
Water shortages do not have to trouble the world if we we start valuing water more than we have in the past.
【翻译】假如大家目前开始比过去愈加看重水，那样水资源短缺就不肯定困扰世界。
我觉得，该句没错。理由如下：
1. 在含有条件句的主从复合句中，假如条件句用一般目前时，主句也用一般目前时的话，表示目前客观存在的情况，不含有将来推断成分。
2. in the past 是一个“模糊过去时间”，跟before 类似，可以跟一般过去时连用，也可以跟目前完成时连用。we have in the past 等于：we have valued in the past。
3. in the past 跟目前完成时连用，举比如下：
In the past this process of transition has often proven difficult.
过去这一过渡过程常常非常艰难。
来自柯林斯例句
In the past conservatives have been in the minority.
过去守旧派一直占少数。
来自柯林斯例句
In the past they have been the target of racist abuse.
过去，他们一直是种族虐待的对象。
来自柯林斯例句
In the past he has pooh-poohed suggestions that he might succeed Isaacs.
过去他对自己会接替艾萨克斯之说嗤之以鼻。
来自柯林斯例句
