> you'd need different prices for different types of consumers

Water shortages are a policy choice in any country above middle income. A simple x gallons for free per person or residence and market pricing thereafter would solve the issue for 90% of the spectrum, with potentially agricultural subsidies filling the gap. Instead, we choose a regressive policy system where individuals subsidise almond farmers.

> Given that there's numerous cities and countries that are suffering from water shortages, you'd think that the price of water would go up already. But it hasn't, because there's interests at play to keep the price of water relatively low.

That just means the shortage is not sufficiently severe to cause prices to move.

> Anyway you'd need different prices for different types of consumers, because it's a basic need for humans; you can't make water unaffordable for poorer people.

The simpler way is to give poorer people money.

The price of water can't go up significantly because the marginal cost of water to farmers is lower than that to residential consumers. Its a lot easier to buy out a few farmers than to take the political hit on high residential water prices.