Water shortages do not have to trouble the world if we we start valuing water more than we have in the past. 

【翻译】如果我们现在开始比过去更加重视水，那么水资源短缺就不一定困扰世界。

我认为，该句没错。理由如下：

1. 在含有条件句的主从复合句中，如果条件句用一般现在时，主句也用一般现在时的话，表示现在客观存在的状况，不含有未来推测成分。

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，也可以跟现在完成时连用。we have in the past 等于：we have valued in the past。

3. in the past 跟现在完成时连用，举例如下：

In the past this process of transition has often proven difficult.  

过去这一过渡过程常常很艰难。

来自柯林斯例句

In the past conservatives have been in the minority.  

过去保守派一直占少数。

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