For watercolors:

First of all, I would like to remember that the watercolor technique was already used in Egypt 4.000 years ago and it is still safe on papyrus!

So, to keep your watercolor safe for many, many years, you will need to frame the art piece with glass in the front and I recommend to use a Passepartout, the French term for a cardboard sheet with a cutout, which is placed under the glass in a frame. To close and protect the back of the frame, please use a sealed 100% acid-free cardboard or any other specific hard material with fungus-free protection.

Never allow the natural or artificial light goes direct to the painting, it will burn the watercolor pigments and consequently fade away their color tones.

For acrylics:

Like any other painting technique on canvas, it will last long but not for ever intact, like the Italian Renascence master pieces, it will happen to have the craquelé – minimal cracks of the painting surface due to expansion and contraction of the painting layer and the canvas – it is the most typical aging effect.

The acrylic technique I use will resist better because I apply a finishing varnish to protect the painting layer, but you also need to consider not to expose the painting on direct sun light or in a room which temperature changes a lot and quickly from cold to hot and vice-versa.

Never clean the painting surface with detersive, use only smooth cloth and dry.

Final advice:

My art pieces should be handled and treated cautiously, like any other fine art, never like ordinary pieces of decor.