Why should alkalis be treated
with care?

because they are very reactive with non metals and some like Potassium and sodium can even burn in air.

Explanation:

Kidneys filter water as Kidneys filter the substance that enters our body using water because water dissolves these substance and send them out of our body. The universal property of water plays a important role in this process as it wash out a great portion even all the substance in our body.

So kidneys filter water and the universal solvent properties plays a important role  in that process.