update_bill.php

<?php

if (isset($username = $_SESSION['username'])) {

$req = mysqli_query($var,"SELECT users.id, users.username,users.daily_consumption,users.monthly_consumption,users.weekly_consumption, valve.water_flow FROM users INNER JOIN valve ON users.id = valve.v_id");

        while($dnn = mysqli_fetch_array($req))
        {
                $weekly_consumption = $dnn['weekly_consumption'];      
                $consumption = $dnn['monthly_consumption'];
                $dailyUsage = $dnn['water_flow'];
        }
        $weekly_consumption = $weekly_consumption + $dailyUsage;
        $monthly_consumption = $consumption + $dailyUsage;

        $updateData = mysqli_query($var,"UPDATE users SET username, daily_consumtion=$dailyUsage, monthly_consumption = $monthly_consumption, weekly_consumption=$weekly_consumption");
}

?>