Dependent fields yii2 - yii2

Question

I need 2 dependent fields in framework Yii2 Example:
I want when i insert in "Numero de Personas"= 5 or other numeric value, automatically "Consumo de Agua"= 2 * "Numero de Personas" = 10.
I saw onchange yii2 but i don't know how use it, i think onchange yii2 is an alternative.
<?= $form->field($model, 'NUM_PERSONAS')->textInput(['maxlength' => true]) ?>
<?= $form->field($model, 'AGUA_CONSUMO')->textInput(['maxlength' => true]) ?>
Update:
With 2 calculated fields example:
$("#consumo-form #{$aguaId},#consumo-form #{$personaId}").on("keyup", function (e) {
var persona = $("#consumo-form #{$personaId}").val();
var agua = $("#consumo-form #{$aguaId}").val();
$("#consumo-form #{$indConsumoAguaM}").val(persona*agua)
});

Answer 1

Here is the approach i would use:
in your view:
<?php
$personaId = Html::getInputId($model, 'NUM_PERSONAS');
$aguaId = Html::getInputId($model, 'AGUA_CONSUMO');
?>
<!-- Begin of form -->
<?= $form->field($model, 'NUM_PERSONAS')->textInput(['maxlength' => true]) ?>
<?= $form->field($model, 'AGUA_CONSUMO')->textInput(['maxlength' => true]) ?>
<!-- End of form -->
<?php
$js = <<<JS
$("#my-form-id #{$personaId}").on("keyup", function (e) {
var persona = $(this).val();
$("#my-form-id #{$aguaId}").val(persona*2)
});
$("#my-form-id #{$aguaId}").on("keyup", function (e) {
var agua = $(this).val()%2 == 0 ? $(this).val() : $(this).val() - 1;
$("#my-form-id #{$personaId}").val(agua/2)
});
JS;
$this->registerJs($js);
With that, both fields will try to auto-complete after the other being changed. But, just to be safe, we need to add a validation on model's rules also.
In your Model:
public function rules()
{
return [
// Your rules
[['NUM_PERSONAS', 'AGUA_CONSUMO'], 'checkValues']
];
}
public function checkValues($attribute)
{
$persona = $this->NUM_PERSONAS;
$agua = $this->AGUA_CONSUMO%2 == 0 ? $this->AGUA_CONSUMO : $this->AGUA_CONSUMO - 1;
if ($persona != $agua/2) {
$this->addError($attribute, 'Error message');
}
}