Basically copy coupon, view price history or create e-mail price alert. Let’s see what best price is ATM.
reverse osmosis (RO) technology, 4 filters: A cotton filter, two activated coconut carbon filters and an RO membrane, 4 filter level has a deep purification, 400 gallons of water a day, 1L / min, Package Contents: 1x Xiaomi Water Purifier, 4x Water Filter, 1x Stainless Steel Faucet, 1x Faucet Valve
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($431.99): BGHONEY2110
2. ($470.99): 7bcdf9
apply code in your basket (cart) after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): e2bcea, 9f65fb, PICODICOM, BGPurifier, AFfbG10, BGWP600G, BG7589, bGhOnEy10, BGYJ001, bgshOOp10, BgoFErTaSchInA10, BGCuponation10
(system checks these coupons on every price check (like once per 24 hours), but you can check them out anyway)
Price history and price alert
Check out price history chart (for all/most countries) for Xiaomi Mi Water Purifier.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).