貯金 = to put money in the bank

節約 = to avoid spending money (i.e., to make food rather than eat out)

Both of these are [漢語]{かんご} (Chinese words in Japanese).

貯金 follows a verb-object pattern. Thus,

 貯(v) store  金(object) - money

節約 follows a duplication pattern:

 節(v)  -save 約 - save

So you can do lots of things to 節約, but if you are talking about water, people say [節水]{せっすい} or about electricity [節電]{せつでん}. In those cases, it means "reduce use of X"

貯金 = to put money in the bank or a piggy bank or envelope.

節約 = to avoid spending money (i.e., to make food rather than eat out)

Both of these are [漢語]{かんご} (Chinese words in Japanese).

貯金 follows a verb-object pattern. Thus,

 貯(v) store  金(object) - money

節約 follows a duplication pattern:

 節(v)  -save 約 - save

So you can do lots of things to 節約, but if you are talking about water, people say [節水]{せっすい} or about electricity [節電]{せつでん}. In those cases, it means "reduce use of X"