Water collected between towers

Question

I recently came across an interview question asked by Amazon and I am not able to find an optimized algorithm to solve this question:

You are given an input array wh

Answer 1

Here's my attempt in jQuery. It only scans to the right.

Working fiddle (with helpful logging)

var a = [1, 5, 3, 7, 2];
var water = 0;

$.each(a, function (key, i) {
  if (i > a[key + 1]) { //if next tower to right is bigger
      for (j = 1; j <= a.length - key; j++) { //number of remaining towers to the right
          if (a[key+1 + j] >= i) { //if any tower to the right is bigger
              for (k = 1; k < 1+j; k++) {
              //add to water: the difference of the first tower and each tower between the first tower and its bigger tower
                  water += a[key] - a[key+k];
              }
          }
      }
  }
});

console.log("Water: "+water);